Nah its not so much problems with the editor -- the editor itself is rock-solid stable (heck that's the entire point of UE3)... the problems people have are the stupid implementations Epic made with the editor to be more Vista savvy (rightclick editor... which means for XP you need to do some rigamarole just to even turn on the editor; another issue of course is the My Documents maps... a lot of people would prefer to have their maps appear in places they want it to)

Nitpicky but still things Epic really needs to change.