Lion stuck in single application mode

I just upgraded to Lion (10.7.1) on my Mac Pro and for some reason whenever I switch between applications, it automatically acts as though I have selected "Hide Others" and hides all other running applications. This is driving me crazy since I have a 27" monitor and normally keep mail and IM visible at all times. Does anyone have any suggestions on how I might fix this? I haven't been able to find anything about it online.

 

I figured this one out. It was Quicksilver. When I updated to the latest version for Lion compatibility, for some reason it automatically turned on one of the extra features that hides applications. The setting can be turned off by going to Quicksilver preferences, Extras, unchecking "Hide other applications when switching". I don't know why it would turn this on by default.