| I (being a Linux-supporter) will attempt to explore this issue in an impartial way.
1. The underdog:
Linux is, and has been for some time, the proverbial 'underdog' to Microsoft Windows. Typically, people have no problem with cheering for the underdog in a competetive situation, but those cheering for the favorite generally are regarded unfavorably. (Note: I know this is something of a generalization but, I believe it holds true often enough to be used for the sake of arguement.) Anyhow, this is one of several reasons that much of the online community (not most, note) favors some flavor of linux in argumentation, and often in use.
2. Linux Bashing:
Microsoft does its own fair share of linux bashing. Speeches by Microsoft and its representatives have not only attacked linux itself, but the GNU, the license behind all sorts of free software, Linux included. Pages on Microsoft's website present all sorts of biased accounts of why, say Microsoft Windows NT is a better server OS than Linux. This hostile attitude from a monopolistic corporation (this argument brought to you by the United States DOJ.) with all sorts of resources and billions of dollars cash generally brings an equally harsh reaction from the supporters of Microsoft's competitors.
3. Nobody likes a bully:
This is a self-explanatory situation exemplified in sections 1 and 2.
4. Trend:
Sadly, it is becoming trendy to bash Microsoft of late. I say sadly (as a linux supporter) because this lends itself to a negative image of linux (and other open-source programs) supporters. As such, trolls on forums like everything2 and slashdot feel a compulsive desire to bash Microsoft and anything thus related.
I hope this covered most of the reasons for the recent flood of Microsoft bashing. Before I get trolled or get negative and violent email please, recall which side of the issue I'm on. | 
