The Bifferboard looks cool. A 150 MHz 486sx with 32 megs of memory is more than enough to run a web server. Heck, I have Drupal running on an m68060 Amiga with NetBSD, and I'd guess that'd be about the speed of a 150 MHz 486sx (although the Amiga has more memory).
The Sheevaplug type machines are good because they don't rely on other things besides some USB storage (unlike that webservusb, which is just a marketing gimmick and useless). I have a Dockstar (same basic chipset as Sheevaplug) running NetBSD and with a 1.2 GHz StrongARM you can pretty much run any kind of web software you want.
Email is a different issue. If you're willing to invest the time (a LOT of it), you'd have much more control over your own email than if you went with Gmail. I started hosting my own email back in the '90s and will never give it up because services like Gmail, Hotmail and Yahoo do certain things terribly wrong (like content based filtering) and therefore cannot be considered deterministic. When my machine does filtering (based ONLY on the sending server), everything gets logged and reported, so it's entirely deterministic. I require that.
Would I recommend it to just anyone? No. If you need or really want deterministic email, then the kind of people who'd play with Amigas would probably do better than most.
