Nothing major so far.
Radiator hose sprung a leak shortly after I bought the car.
A few electrical problems that I attribute to Saab quirks... central locking works intermittently.
Intermittent wiper setting doesn't work.
Light in instrument cluster hasn't worked since I bought the car... I've gotten used to it.
The A/C sometimes shuts itself off, possibly a fuse problem.
Headliner sagging above driver's seat.
The old 900's have a distinctively quirky look and personality that sets them apart from most other cars on the road.
I wanted a car that didn't look like everyone else's and knew I couldn't go wrong with this one.
Driving this car is an absolutely wonderful experience... the backward mounted 2.1 liter 4 is still pretty smooth for its age and mileage. I initially had reservations about the 3-speed automatic because I'd heard that they tended to be troublesome. Mine has been OK so far.
The paint job is practically flawless and there's no rust to be found anywhere. The interior is in mostly good shape, aside from the saggy headliner (a common 900 problem). The cloth upholstery is still nice looking and the seats are still firm and comfy.
Handling is great and the ride is nice and firm, though it can get a tad harsh on rough roads. Braking is excellent.
Overall my 900 is still in pretty good shape. I love the turn signal cornering lights at night and the side lights that come on when you shift into reverse... I feel like I'm landing a spaceship.
If you want a truly unique car that strangers will compliment you on then definitely consider a 900. Just be ready for a few eccentricities.