Change, even from bad to good, is never without confusion, inconvenience and problems. Hence, the decision to skip Windows XP or Vista and move to Windows 7 will not a smooth ride. Do not expect it to be one either.
Those who run Vista would probably have switched to Windows 7 by now. The latter is all that Vista wanted to be but could not be. Vista had many flaws, problems and was widely panned for not being user friendly. Windows 7 is all that and more. Hence, if you have Vista, then the only factor you have to worry about when switching is the cost factor. Vista is inferior to Win in all other aspects.
The real confusion begins when one compares XP with Win7. People have come to love XP over the years. They are very comfortable with this OS and see no reason to use any other OS, even if it happens to be a new and improved one.
However, there is no denying that Win7 is the way to move forward. There is no denying that XP is a very good OS. However, the latest OS too has its share of good features and, more importantly, does not have too many flaws and complications. Hence, switching from XP to Win7 will be switching from one good OS to another very good OS.
Unless you have very good reasons to continue using XP, you should switch to the newer OS. What is more, Win7 offers the XP mode where you can run your XP centric programs as if you have the same OS installed in your computer and as if the newer OS has not be installed at all.