Sometimes I surprise myself. I have no Microsoft software installed on my office computer. I have Microsoft Windows Vista on my laptop, because it was pre-installed, but it is in a separate small partition that I almost ever use. I detest Windows, and have detested it since it was a separate program that one used by typing "win" on an MS-DOS computer. (Actually, I have rarely used it since those days.)
But a couple of days ago, I set the default search engine on my Firefox search box to Microsoft Bing.
I've been going back-and-forth between Bing and Google for a while, and not only does Bing look nicer and show up a useful mouse-over preview of search results, but the results look mostly more relevant. Most of my searches are academic-related. I still have the Google toolbar installed, with its own search box, so I can easily go back and forth. When searching for scholarly articles, I use either Google Scholar or PubMed -- so far there seems to be no Microsoft equivalent of those, but I won't be surprised if it's on its way.
I used to be a free software idealist, but the question is somewhat moot with online services. Besides, I have figured out now that what I really want is customisability. (This is also the reason I was never very tempted by Apple.)
Linux is almost infinitely customisable, but the days when I would build my own kernel and compile much of my software from source are long over. Nowadays it's just a question of selecting from the options in Ubuntu's software repository -- and, in rare cases, enabling an external repository.
Now, suppose my next computer is pre-installed with Windows 7, and it turns out that I can configure it to a unix/X-like interface with my own key bindings and can install most of my favourite open-source software, pre-built, with a few clicks (as I can in Ubuntu): would I consider going with it, and not repartitioning and installing some form of Linux? Till recently, I would have laughed at the idea of Microsoft becoming so open-source friendly: but the world is becoming a strange place now.