Having googled extensively over the last couple of days and found nothing useful (but I did find several people with the same problem) I thought I’d come back and explain exactly how I sorted the problem, now that I’ve actually sorted it.

First things first. I bought an Acer Aspire One (D250-1924) from B&H Photo while holidaying in New York last week. Note with all the below I am referring to the integrated trackpad and mouse buttons. I do not use an external mouse or keyboard. The click in the left mouse button lasted precisely 4 days before the button would no longer click and to register a left mouse press in windows, you had to press unreasonably hard on the left mouse button. The click in the right button remained and it continued to function as expected.

Knowing well that Acer would most likely no honour a warranty claim on a US bought device in Ireland, I went about fixing it myself. Before anyone points it out, yes, this will void your warranty and I only carried out the fix because I knew what I was doing, my warranty wasn’t worth toilet paper anyway and I didn’t want to pay nearly half the price of the netbook again in repairs charges for something I could do myself. The photos aren’t great by any means (can I have a macro mode in the iphone please?) but same goes for all of them, you can click for a bigger version.

First, take out the battery, then remove the three screws underneath it. Remove a further 7 screws from the bottom of the netbook as shown in the photo below (3 top, 4 bottom).
Screw locations underneath netbook

If you open the memory door, you’ll see another screw to the top right side of the compartment. I don’t know for sure if you have to remove this or not, but I did just in case.
Memory Compartment

Flip the netbook over and remove the keyboard by placing a thin flat screwdriver between it and the keyboard surround. They keyboard is secured at 5 points by clips. The approximate location of these clips are; next to the left ctrl key, just below the escape key, between the F7 and F8 keys, to the right of the delete key between delete and backspace and to the right of the page down key, as shown in photo.
keyboard clips

I recommend unclipping them in the order of top of the keyboard to bottom as the end of the keyboard is also secured by metal pins in slots so if you unclip the keyboard from the top and sides first, it’ll lift out with some ease.

Be careful when lifting out the keyboard as it’s connected to the motherboard by a ribbon cable. Gently lift the locked ends of the connector and the cable will slide out, allowing you to completely remove the keyboard. Ribbon cable and connector to motherboard shown below.
keyboard ribbon cable

There are several screws, similar to those already removed, underneath the keyboard. Remove these also. There are also several smaller ribbon cables and connectors connected to the motherboard, plainly visible once the keyboard is removed. You need to unlock the connectors and remove the cables before removing the top of the netbook. The locations of the screws are shown in red and the connectors in blue.
screws and motherboard connectors

Once all the cables are disconnected from the motherboard, you can start to remove the top of the netbook by gently lifting it from the back (where the Aspire One logo is). There are clips holding the top down, two on each side, one on end either side of trackpad. I needed the flat screwdriver again and put it between the bottom and top parts of the case to pop open the clips. A little force is required to get the clips to pop, but as always, be careful.

The top of the netbook will lift off with some gentle wiggling and pulling. There are several sticky foam pads (such as those around the inside of the trackpad hardware holding the device in place and cushioning it) and these will become unstuck as you pull.

Once the top is off, you’ll be able to see the mouse buttons clearly. The left mouse button is highlighted in the photo below. If you press each with your fingernail and they both make a clicking noise (as mine did) the problem is possibly that the small sticky shim that Acer have installed on the left button has moved.
motherboard with left mouse button

My previous fix, which was to replace the shim and put two tiny squares of sticky tape on top of it to increase it’s height only worked for a few hours until the action of pressing the left mouse button caused the tape/shim stack to move off the center of the mouse button.

My current fix (still in testing but somewhat more solid) was to remove the green sticky pad from the underside of the left mouse button as shown below. I cut two thick pieces of paper (from an envelope) to the exact size of the green pad and put a tiny spot of superglue into the hole I removed the green pad from. I then stuck the two circles of paper into the hole and used a tiny amount of glue to stick the green pad back into hole, on top of the paper. It provided the extra millimeter (possibly not even) for the mouse button to make contact with the switch on the motherboard without having to use the plastic shim.
underside of mouse buttons

Note that the top of the switch on the motherboard for the left mouse button will likely be sticky from the shim. This will cause the green pad to stick to it, leaving you with a very slightly sticky mouse button. Take a small amount of paper and wipe the remaining adhesive off the button so the green pad doesn’t get stuck to it every time you press the left mouse button.

Assuming the glue stays stuck (it was cheap.. very very cheap), I shouldn’t have a problem. I’ll be sure to report back and update this post if I find I need to take any further action to sort the problem once and for all.

I put the whole thing back together, connected the battery and booted up to ensure all devices were working as they should. Hey presto, no more poorly performing left mouse button and no costly repairs for such a stupid problem. As a side note, I can’t understand why Acer use the sticky shim for only the left mouse button. Seems like a design flaw that these things are moving and the mouse button becomes practically unusable.

Note that if you choose to carry out the above fix on your own netbook, you do so at your own risk. If your warranty is still valid, check with Acer if you can have the repair done under the warranty. I take no responsibility for anyone killing their netbooks by copying what I have done above. As I stated above, I only carried out this fix because my netbook has a US warranty and I am living in Ireland. Acer warranty service was not available to me.