I'm a solid week into a switch from Linux to Windows Vista on my IBM / Lenovo T60 laptop and wanted to share my experiences.
I've been a linux user for years now - think slackware distributions on stacks of floppies. In fact, I've been pretty successful at using it for all my day-to-day tasks for several years now, although I'm forced to keep Windows around (on VMware, usually) to run the inevitable bit of software that's just not there for Linux - thinks like Quicken, TaxCut, and MS Access and Visio. Linux is great for geeks trying to get stuff done: coding, running web servers, finding all the phone numbers in 500 hmtl files, etc. It even does an acceptable job on communication tasks: running Lotus notes for work, Word and Excel documents, etc. Where it fell down for me, and had me recently move to Vista for my day to day use is how well it deals with hardware. A year-and-a-half ago I moved from coding to management (although I still find time to code. :-), and with that, I became more mobile and communication oriented. Linux on my laptop worked great - as long as I was sitting still. (At this point you ask yourself, why have a laptop if you have to sit still?)
One of my big gripes was that my laptop would only recognize monitors that were plugged in when it stared, which made hauling it down the hall and plugging into a projector or returning from a meeting and docking back to my desktop monitor problematic. Another is that due to some problem with the way ATI's video driver used SLUB memory management while the latest kernels used SLAB (or vice versa...) meant that my laptop couldn't sleep or hibernate - it was just on or off for me. I'd had enough when it took me 12 minutes to get up and running at a meeting: a few minutes to get linux started (of course it had to pick then to fsck a couple of partitions), then to restart because the projector wasn't on and recognized, then another few minutes to get VMware & Windows fired up, and another few for restarting that because it didn't suspend properly, then to get Visio launched and load the doc that we were editing at the meeting. I decided then and there that I'm tired of the compromises and don't have nearly the time and patience required to fix the problems - I could download and rebuild my kernel (I've done it before...) and solve the sleep problem, but I shouldn't have to do that. I have no idea if the monitor detection problem is solvable by me. It was a hassle on Linux to do things that involved the Enterprise active directory - all that's trivial now. All the fancy networked copiers / scanners / printers / faxes at work now just work.
After reading all the horror stories, Vista has all been a very pleasant surprise.
Anything's possible under Linux, if you have the time and patience to do what it takes to make it work - I have far less of both these days. I still love Linux: it's still my main machine at home, and it makes my MythTV (homebrew Tivo) possible. It just can't make my laptop do what I need it to do to be productive.