We don't have many owners signed up to field qustions on the XC90, so I'll give this a try.
Any European car with over 100,000 has a good chance of being expensive to maintain. The 2010 has been looking good in our stats, but we have a very small sample size for it, so our stat could be inaccurate.
I have heard that the V8 can be very expensive. The six-cylinder engine is a better bet.
Early on XC90 owners complained about the frequency of tire and brake pad replacements. I don't know if Volvo ever fixed this issue.
You might find more on swedespeed.com, a good Volvo forum.