Been using XBMC for a month and it's awesome.
For my main TV I'm using a budget PC connect to my TV using HDMI. Sometimes I use ARC from my TV to my HTIB for better 5.1 sound to get cinema experience. There are many contents in HD and in 5.1 audio and of course new movie or TV show release are available almost up to date.
Mashup contents itself is more than sufficient. There are even 3D movies too and no issue with lagging even with 3D with my VIP10 Unifi.

I also use a Himedia Q5 for my bedroom TV to watch late night sport on Navi using WIFI. Totally satisfy.