The reason for the sludge problem is the exhaust design. The exhaust runs right under the oil pan, which helps to warm it up quicker when it's cold. great idea, except the oil pan gets really hot and you get sludge. If you change your oil regularly, and drain it well, you're probably fine. Synthetic oil will help. Turbo's should be on a shorter time interval than NA engines. 10K may be a on the high side. I've advocated that interval before, but after further research I've settled on no more than 7500 with the synthetics on the turbo, but you can still easily go past 3000 miles. 5K is probably a good number with all those short trips. No oil should be in the car more than a year.
Short trips are bad for the engine, but I have a sneaking suspicion its affects on sludge may be minimal, due to the fact that you never really get the exhaust super hot.
I know Toyota is having real proplems with this, even with people who change the oil regularly. I'm not sure if Saab's problems have been as bad. And they've at least owned up to them to some degree. Doesn't seem like Toyota's been nearly as generous.