So far, the odd numbered ones seem to be the hits.
Windows 3.x took off.
Windows 2000 (that would be 4) was a bit much for folk to get into.
XP (could be called 5) seemed to nail what folk wanted.
Vista (6) was a bit unloved.
7 (7) pulled it all together again.
8 is being force fed to the consumers. Not going too smoothly.
9 looks to be fine.
10 may be like zen. Few will comprehend it.
11 will be heaven according to some.