Comment This happened to me. (Score 1) 429
I dual booted Windows 7 and Ubuntu 9.04 (or 9.10, I don't remember), because I work with Adobe products often so I need Windows but I also like to dabble in Linux from time to time and running either OS in a virtual machine doesn't cut it.
Ubuntu/Windows fucked up my GRUB and/or ext3 partition and I couldn't really find a way to fix it either. I'm not a beginner Linux-user but I am no sysadmin either. I could never get into my Ubuntu system again.
Ubuntu/Windows also messed with the head of scandisk/chkdsk in Windows 7 that it "repaired" my files regularly at reboot which eventually lead to a huge loss of data. (Most of which I got back, fortunately.)
Since then I don't dare to run Linux/Windows dual boot anymore. It's a shame, because I like them both.