MacBook Pro: Shutdown Roulette

The MacBook Pro returned on Monday morning, and since then, I've been extensively using the MBP running all manner of applications to give it a proper shakedown. I encountered some slowness running some apps on Rosetta, but on the whole, the MBP runs them without issue. Since there are so very few apps that can adequately test the MacBook Pro's graphic card, I've been excessively running it through its paces playing World of Warcraft (one of the few Universal Binary games available). The framerate on the system is about 30-60 fps, comparable to other PCs I've used.
I've also been using Final Cut Express to try and edit together a video for the Freeculture contest -- this has not gone well, as FCE is practically unusable with 1GB RAM running under Rosetta -- the performance was so atrocious, I've given up trying to create an entry in time for the contest.
The newest and latest problem I've discovered is a random shutdown of the system for no apparent problem. One minute I'll be surfing the web, the next moment the system is powered off. Needless to say, the Mac is going back to be repaired. For those keeping track, this is repair #3. If it goes in one more time, they'll likely replace it (and I can start this process all over again)