Vista and 7 unreliability
I bought a brand new laptop last Christmas for my girlfriend - she is not computer savvy or anything like that. I tried to install the w7 included on the extra HD partition - crashed 3 times! I said bugger that and installed ubuntu 9.10, works perfectly, never crashes, and has all the applications you could want. Her desktop had Windows Vista, and was dinosaur slow, so I put Ubuntu 8.04 on that, also never crashes, is super fast and no Microsoft bloatware. Everything works together like it is supposed to!