I've basically been using Win7 since it was available (I got the RTM version via our university), and so far I only noticed positive changes:
Libraries are great for accessing multiple locations of similar content. I have all my digicam pictures in one folder. There's another folder somewhere completely different with a collection of pictures of my girlfriend and me. So I just add it to the library and they appear to be in the same folder.
Hard disk image backups are great, not only for backup reasons, but also to migrate a working Windows installation to another harddisk. I installed it on a really old one, and when I bought a new disk, I made a system image, put it on the new disk and my system didn't notably change.
Non-admin user accounts are now actually useful compared to XP. Whenever I need admin access for anything, I just enter my admin account password, and that particular process gets admin permissions, nothing else. Great way to prevent accidental system setting changes.
Defrag now works almost unnoticeably in the background of a running system if you've scheduled it. I don't use the windows defragger right now, but as long as I used it, it was great.
VHD files, hard disk images created by Virtual PC, windows backup or the storage manager, can be mounted like regular hard disks, in normal or read-only mode. Not an everyday feature, but not bad either. Apparently it's also possible to install windows on one of these virtual disks and have a self-repairing system.
Internet Explorer now is an extremely secure and comfortable browser. While it's not exactly a Win7 component, it can use a special secure mode (much like a sandbox) when running in Win7, making it actually safer than most other browsers who don't use this OS feature.
Window management is great. I got so used to Aero snap and stacked windows with previews that I can barely adjust back to XP now. Now it's even more better than Mac OS in this regard.
Some hard- and software I couldn't get working after I switched from Me to XP (a USB IR port for example) are now working just fine again. I had a lot less compatibility problems with Win7 than I had with XP. Actually, I had none so far.
Pinning programs to the task bar is great. Although most Mac users just see this as a lazy copy of the mac dock, it's much better executed in Win7, with jumplists and full, seamless integration into the window manager (the taskbars original function).
System restore seems to work a lot better now. Old versions of any files and folders can be accessed any time you want through a convenient interface. Saved me from the consequences of quite a few accidential overwrites.
Well, there a a lot of nice changes, but also a few disadvantages. The only one coming to my mind right now is the search function, which feels a bit restricted compared to XP.
