I have to agree with Judith, it's a lovely country but to be out and about in a major city like Mombassa as a tourist (ie sticking out like a sore thumb) without taking precautions is unwise. Local guides will tell you to make sure all windows are closed and locked while driving through the city in case you get stuck in traffic or at traffic lights to prevent the snatching of bags and other lose items.
A little crime is a bit of an understatement realy. As I said before, I wouldn't say it's overly violent and the Kenyan people are lovely generally, but there's lot's of poverty and crime is a way of life for some as they are desperate. I gave away t-shirts and a few other things, what's a few £££ to us when the general population can't afford to send their kids to anything beyond primary education (that's state funded). Secondary education is about £150 per year per child, or about 50% of the average salery according to some I talked to.
Darren