OS 10.4 - Mouse moves, can't click anything, system locked.

I posted a thread in the hardware forums and called apple care about this problem thinking it was hardware related but now I am not so sure. I bought my new 24" iMac yesterday and the first place we looked was Fry's and we noticed this symptom on their demo machine and didn't think much of it as it was a display model.

We ended up getting the iMac from the Apple Store and about an hour into setting it up I started having the same problem the iMac at Fry's was having. I could move the mouse around but clicking anywhere on the screen did nothing. Weird little graphics glitches would appear too down by the doc and eventually I would have to hold the power button in to get the system to reset. The system did this a few more times, even interrupting my apple care phone troubleshooting session several times as I had to constantly reset the thing.

So I am reading around the forums here and I see that one recommendation is to create a new profile. I logged in to my girlfriends profile we created (but didn't use) last night and it didn't lock up at all. As a matter of fact, I logged out and back in to my account and I have been running fine for over an hour now. Is this kind of weirdness common? Could it have been a recent software update? Should I still go to my Apple Genius appointment tomorrow if it isn't going to exhibit any symptoms?

Thanks for any advice and for reading my long post.

*** EDIT *** The problem returned on my profile. I just hope it acts up at the store tomorrow or they take my word for it and replace it.