With Windows XP/2003 and earlier you could often just look in C:\windows for installed patches there would be a KBxxxxxxx folder, however life moved on..
Today I had the need to see if a patch was installed and I found this quite useful;
I ended up using the command;
wmic qfe | find "KB2744129"
You ofcause exchange the KB number with the one you are looking for..
This worked like a charm for me :-) tnx Jscott.