If I had to bet on one starting goalie from last year posting a lower save percentage in 2010-11 than he did in 2009-10, I'd pick Jimmy Howard.
All the signs are there for a regression. First of all, Howard outperformed on special teams. He had a very good save percentage on the penalty kill (.905, 4th among starting goalies), and he faced a low percentage of shots against on the PK to begin with (16.0%). He only let in one shorthanded goal on 50 shots against while Detroit was on the power play. Put all that together, and the result is that Howard's even strength save percentage (.925) was nearly equal to his overall save percentage (.924), something that is rare and generally not sustainable in the long run.
For any goalie with essentially one NHL season under his belt, it's best to look at their minor league performance to see if there is a track record of success. Howard played four full seasons in the AHL from 2005-06 to 2008-09, where he compiled a .911 save percentage on 5,324 shots. That's not bad, but it's nothing that suggests future NHL stardom either. Howard's backups combined for .895 on 4,171 shots, so perhaps there is some evidence that Grand Rapids was not the best defensive team or took a lot of penalties or has a miserly official scorer, but I still don't think Howard's minor league performance is at a sufficient level to foreshadow a future elite NHL starter.
None of Howard's AHL seasons were more than .005 above or below that .911. There's not a clear improvement trend in his numbers, which means that I wouldn't put it at all out of the realm of possibility that he might be a similar goalie in skill level now to what he was the age of 23 or 24. His ascension probably had as much or more to do with spots opening up ahead of him in the organization as with the development in his own game.
It's pretty obvious that the Red Wings themselves didn't think Howard was anything special until very recently. Why else would they have signed Ty Conklin in the summer of 2008 to back up Chris Osgood during the 2008-09 season? Howard was 24 years old with three full seasons in Grand Rapids under his belt at that point, and his own team still didn't rate him as good enough to be an NHL backup. Having said that, the Red Wings are known for their patience in developing prospects, so perhaps it was entirely a matter of maximizing Howard's playing time, but regardless he didn't exactly force his way into the NHL either.
I'm not willing to make the argument that there are strong team effects boosting Howard's performance without a lot more data, but on the other hand I don't rate playing behind Nicklas Lidstrom, Pavel Datsyuk and Henrik Zetterberg to be one of the league's toughest assignments either.
Excluding the 2009-10 regular season, Howard's career NHL record is .912 on 614 shots. That's a tiny sample, but I think it's still probably more representative of Howard's true skill. Puck Prospectus' VUKOTA has Howard projected at a .914 save percentage next year. Guys who have great years are likely to regress somewhat the following year, that's just basic sports statistics. If they don't have an established track record of success either, then the indicator lights are flashing even more strongly. I'd say Howard is more likely to have a below-average save percentage (say, .905-.910) than he is to match his .924 this coming season.
There is of course some small chance that Howard either legitimately became great or his run of luck continues and he remains near the top of the save percentage leaderboard, but it's certainly not the way to bet. It will be interesting to see whether his performance over the next couple of seasons indicates that he is anything special or just another guy at the NHL level.