This is just my personal read on the situation, based on nothing more than casual observation and rampant speculation...but I think something is up at USC. Not necessarily something sinister on Carroll's part, but I think that he sees rough times ahead for the Trojans. One theory is that Carroll might see some penalties for recruiting violations coming down the pike, followed by NCAA sanctions. He has been very lucky to have come out unscathed amid some major accusations made against the USC program and their boosters in recent years, including allegations regarding Reggie Bush and Joe McKnight. Imagine if the same rumors were swirling around Miami or Alabama, Sports Illustrated would have been calling for a death sentence for 4 years now. The NCAA has already caught up with the USC basketball program, and although there is no reason to suspect that Carroll had anything to do with these incidents (he is by all accounts a stand up guy) it would foolish to believe that he alone could prevent the types of impropriety alleged. I think Carroll is reading the writing on the wall and is attempting to make an early exit before the s&#t really hits the fan...much like John Calipari did at Memphis. Unfortunately for USC, I think it has been Carroll's reputation and demeanor that has held the media at bay for this long.
Everyone is asking the question, "why now, and why the Seahawks?". It is beyond dispute that USC is currently the premier coaching job at the premier football school in the country (sorry golden domers, you're delusional). Carroll, a well known "surfer dude" is the de facto king of football in Los Angeles, a setting that seems perfect for his lifestyle and persona. Of course it's possible that he just got the itch to make it in the pros, but he's had other, more attractive offers...including the Miami Dolphins in 2006 and undoubtedly countless inquiries from other teams over the years. While Seattle is a great city with great fans, and an unbelievably loud home field...the timing seems a little odd, and the destination just doesn't seem to fit.
Best of luck to you Pete, the college to NFL jump hasn't been an easy transition recently, and I don't know how full the cubbard will be for you in Seattle...but if this causes a few stud USC recruits to look elswhere and spread the love, then I'm all for it.