By 2010, which was the last year of the e83 x3's, most if not all of the previous issues with the x3 were ironed out. The earlier models (07/08) had some issues with the auto tranny that caused harsh up/down shifting on inclines and declines but I haven't heard any complaints from the 2010 crowd about this issue as I believe something was replaced in the later years to remedy the problem.
Other than that they have similar issues as the three series which aren't too bad. I'd think about doing a complete driveline fluid change if you do end up picking it up and ensure you go with the BMW fluid in the transfer case. The drivelines aren't known to be that robust on the x3 but with servicing they should be fine.
X3's also have a common fault that is pretty rare as far as I know which is the rear springs break and need replacement. They aren't too expensive and are relatively easy to fix.
The 3.0i got the n52 engine which i what mine has as well. I find it a really nice drive and fairly reliable with the exception of some common oil leak areas which aren't anything to worry about (typically valve cover gasket and oil cooler gaskets).
Most people online tend to hate the x3 but those who actually own them tend to love them or at the very least have a love/hate relationship with them. They are undoubtedly one of the best handling "SAV's" on the market and I've really enjoyed mine despite the tranny problems I encountered that I outlined earlier.
Also, from my experience, http://www.bimmerfest.com/forums/forumdisplay.php?f=65
is the most active e83 forum around and has a wealth of info and knowledgable members to help answer questions.