I just upgraded from XP to 7 Ultimate 64 bit. I like Windows 7 a lot, particularly after I got everything tweaked the working the way it's supposed to. It runs very smoothly, and has a great way of monitoring your system and offering solutions to problems. Overall, it is the best Windows operating system and I am glad to have upgraded from XP.
With that said, I haven't seen a big reason to upgrade if you are unsure about it. The internet is the same, e-mail is the same and still clogged with spam. If you have older hardware, particularly a buggy hard drive, you will run into problems with Windows 7 and it's indexing service. If you have an older Creative sound card (Audigy 2 for me), you will lose much of your EAX and audio functionality. Older software will not work, for example I lost my Palm Pilot desktop in the upgrade. Finally, don't think that all your games that played so well on XP will automatically work on Windows 7. Fallout 3 for me took quite some time to get to work properly, and that is a common complaint.
So, in short, I would say Windows 7 is the way to go, but don't think that it will just be "plug and play". You may have to spend some time to get everything working just right. If you are unsure and don't want to upgrade, then you are basically only missing the slick Aero interface and some of the more advanced system monitoring capabilities. In the end, though, it's just a matter of time before you will need to upgrade...