Re: XBMC & Media Hubs
XBMC on the Pi (OpenELEC, Raspbmc, Xbian etc.) can play back full high-profile Blu-ray rips so I don't know what you're on about saying it can't handle MPEG4 HD, that's utter FUD.
I've also no idea about your DVB-T stick, maybe get one with decent Linux driver support next time - plenty of others are using their Pis with XBMC for Live TV/PVR viewing.
The Pi with XBMC does actually make a genuinely good "media box" - it can pretty much play anything you care to chuck at it, either from local HDD (USB attached), from your NAS or streamed from the web.
Sure, the ARM CPU hasn't got the same slick performance as a quad-core i7, but the GPU in the Pi is surprisingly powerful and funnily enough that's the most important thing when playing hardware accelerated videos. And despite being low powered, the ARM CPU still provides a pretty good user experience when browsing around the menus and library in XBMC (officially sanctioned overclocking to 1GHz+ helps improve the UX, of course).