I wasn't wowed by the warehouse, but if you really want a Disney-themed shirt, aren't terribly particular about who is on it, and don't mind paying a fair price (I think the ones I saw were mostly $15), then it's a good place. They had a pretty good selection, but I couldn't find anything I liked enough to spend the money on, so I went back empty-handed. I actually preferred the character store in a mall a few hours outside of Orlando to the one just a few miles from
Disneyland, as I was even able to get an Epcot shirt for $3! Oh well.
If you decide to go to the one in Fullerton, here is a coupon. It is in the same plaza as Dollar Tree so you can buy glow necklaces/bracelets too!
http://www.thechamber.net/cgi-bin/foxweb.dll/wlx/dir/wlxcpn?ec=lbyklLsiprtbx4mpmc&ID=HNDgKiGb