Ron Reisingner pointed out three issues of Windows 7 in his article-What scares me about Windows 7:
More for Mac users than Windows users-Microsoft's quest to make Windows "prettier," it sometimes makes it harder to perform basic functions. The same Windows you're familiar with is still there, it's just harder to find under all the makeup. Especially if you're an XP user who skipped Vista.
Security issue--Windows 7 is about as secure as Windows Vista, which was plagued by 639 threats over a six-month period. That's an improvement over previous iterations of the software, so sticking to XP probably isn't advised if security is a major concern, but let's face it--that track record isn't ideal.
Long learning curve--unless you're a Mac user or a Vista convert, it will probably take some time to get used to Windows 7
Praised by same author Why I can't get enough of Windows 7