It is a pretty easy fix. Some A-Buttons have a small plastic blob inside from moulding (only the A-Buttons, weirdly enough).
You just need to scrap that plastic off with a screwdriver and that's it.
Only issue is that you need to open the unit.
Yeah, I had this problem with my "A" button being spongy, and I described this fix awhile ago, and I hoped it would be addressed by the team, or they could pass the info to the mould factory. But I'm sure the first 4000 had been done by the time it was figured out what was causing it. So I guess it should be fix by Craigs team at assembly.
The A button functions perfectly but as it has been said, but it doeasent have that click like the others. It bothered me, so I opened the unit to try and find the problem. Once you carve out that excess plastic under the button, it works perfect, just like all the others.
It was very easy for me to do myself, but I have experiance modding DS/PSP's, so it wasn't hard for me. If you have a good comfort level around small electronic devices, it should be a breeze. DO NOT ATTEMPT if you are not comfortible in this area, or have no idea what you are doing. There are many small items that could be broke if you don't know what to look for, and it would suck to break your unit just so you could fix a small button defect. Hopefully Craig's assembly team will begin to check all 4 buttons for that excess plastic and remove before assembly, but I would imigine thousands of button could take awhile to notch out.
EDIT:1 person with a dremel tool could probably check all the buttons, and have them done in 1 day or less. Maybe it was detemined that since the button works, it's not a problem, but I found it annoying that one button functioned slightly differant than the others. Maybe it can be addressed while they wait on more boards to arrive? Who Knows!
Chris