Sysadmin here:
We've migrated about 50 users (salesforce, most are aged 40 to 60) to Win7 from XP about 2 months ago. Here's what's happening for us:
* No major problems adjusting to Win7 (I've had a couple of quick questions, that's it).
* Running users as standard users is almost viable (we're having a lot of pain and suffering from all the crapware we have to install (Adobe Flash, Reader, Shockwave; Quicktime, iTunes; Java; etc, etc) -- almost everything on this list wants admin rights to update itself). Users can't install much or tweak much, so much less user-induced OS failure/slowness/malware. We're trialling SCCM for this, so we'll see...
* Win7 seems less prone to malware infection. I doubt it's anywhere near secure, but it's already doing a lot better than XP. (I'm forced to use Symantec for AV, which is about as much protection as a pincushion condom.)
* Device drivers for modern PCs on XP is a royal pain; Win7 is ok for now (a couple of bad device drivers for Win7 x64, but much better than XP x64 and good enough for use), and updating device drivers from Windows Update works about half the time.
* Imaging tools are much nicer.
* Sleep and hibernate seem to be more reliable. XP would fail to resume 1 in every 200 resumes or so.
So for us, Win7 is a major step up -- it isn't that it's good so much as it sucks much less than XP (which sucked much less than 98, etc.). Furthermore, ReactOS (last I checked) is far, far, far away from being a viable replacement. MS could sit still for 5 to 10 years and ReactOS would still be far away. Give those guys several more good programmers and the story might be different...