Why Fvwm?
It is something that i get asked quite often, mostly followed by a remark about it being extremely ugly and outdated.
Both of these are untrue. The default config, indeed is pretty bare and, yes, it's probably not everybody's cup of thea, but there are still people that actually like the Motif look of it. That being said, there is an initiative to provide a new default configuration for Fvwm, you can read more on it here.
The other statement, Fvwm being outdated, is easily countered, Fvwm is under pretty active development, new versions still appear every so often. If referring to the looks with outdated I would recommend you check out some of the configurations I link to, or my own of course, so you can see for yourself that it is possible to make Fvwm look the way you want it to.
Indeed, you can make Fvwm look like about everything you'd ever want it to look like, Fvwm's nearly infinite configurability allow you to build a configuration that is tailored exactly to your needs. This configurability comes at a price though, Fvwm isn't the easiest of window managers and if you don't like reading a lot in manpages and on websites to get things set up the way you want you're probably better off using some other window manager, like for example Window Maker.
Now, how did I get to know Fvwm to start with because, nowadays, one deosn't hear about Fwvm a lot, indeed, I very often hear from people that had never heard about it at all.
I first ran into Fvwm on my RedHat 6.0 install, which was also my very first GNU/Linux installation ever, when I was testing all available wm's. The Fvwm I then met was the fvwm95 incatation, and I didn't like it, so I went back to using WindowMaker.
Some time later I read Michael Hammel's "The artist's guide to the Linux desktop", which is where I first read about Fvwm's configurability, I immediately rushed to try it, but that didn't work out very well, I was still too new to Linux and the information in the manpage was a bit beyond me... So I once again returned to WindowMaker, then i got a faster computer and moved to Enlightenment DR16.
By this time i had also dropped RedHat in favour of Gentoo and then I came accross a post by Tavis Ormandy about Fvwm, I immediately dug up my old LinuxJournal issue and installed Fvwm, this time I was prepared for it and I've been using it ever since.