Plex is branch of XBMC. Originally dedicated to work specifically on Macs, but futher developed to more platforms.
I used another xbmc branch for a while - Boxee (PC) and frankly I was mostly happy, however there few things most PCs still don't do :
* Very low power consumption (during both operation and idle)
* Instant Power On/Off (usually pc's do ether a or b, but not both)
* easy and full remote control
* full silent design
* support for BDMV ISO and HD audio codecs
In the end I think my current Netgear NeoTV-550 does all that at hard to beat $100
Is it [STRIKE]idea[/STRIKE]
ideal product - no, I personally not big fan of it's menu system and even adding more movie graphics and tags didn't improve things much...
For example one of things really bugging me - it does not separate TV shows from movies, but excellent codec support and stable and silent operation make up for most of it's flaws, I just do folder playback