It is more than one week after I upgraded to Android 2.2.1. The issue with disappearing / removed SD card problem is gone.
I have LG P500 Optimus One Android Phone with Kingston SDHC 16GB Class 4 card. Before upgrade I had a more than a couple ‘SD card unexpectedly removed’ errors per day. Also, random reboots was a norm. Now, one week after update – no single issue. So LG update to Android 2.2.1 resolved this issue for me.
The strange thing is, that some people still report this error on Android v2.2.1 on Google Android project bug tracker. See Issue 9736 – SD card unexpectedly removed error LG Ally.