rex is my favorite toy story character. when i saw this at target, i had to play with it. the one i played with had an AWESOME roar! and it amused me for a good 5 minutes or more while my partner was looking at something else. i reaaaaallly wanted to get it, but she wouldn't let me. not a valid purchase for an "adult" i guess.
it was the only one there, so i couldn't compare one rex's roar to another's, but i can see how if the "floor model" were played with too much, or treated badly, you could take home a dud. it's also likely that some shoddy "diaphragms" as another reviewer called them are out there. so, best bet is to buy this in person so you can test out the ROAR! before you take it home.
if you get a good one, it's totally sweet, and will amuse your inner child as well as any "real" children that may be around!
3/19/11 update: i have seen a few more of these at different stores now and most of their roars are pretty weak, which is very disappointing. perhaps it's because they've been on the shelves longer and played with more?