Yup, I'm in the "a single audio and video system in a multi-purpose room" section.
It's my living room, and I use it not just for the HT, but for socializing and eating meals. It's a 27" SDTV (HDTV coming hopefully in a couple months), A/V receiver, 6.1 setup, DVD player, VCR, record player.
To tell the truth, a sub upgrade would be brilliant for me. Whenever there's an album playing that has lots of bass or a movie with explosions or whatever, I always take a glance at the sub, and sure enough the light is on, indicating the sub's receiving a signal, but I wonder just how much it's giving me. It's level matched plus 2 dB, but still I sometimes feel it's just not giving me much (despite SheepStar's review). Anyway, an upgrade might be really sweet.
I do have a PVR video card in my computer, but I don't really consider my computer another video system. I mean, it's just a 19" monitor, 2.1 sound, and analog cable signal. Nothing fancy -- certainly nothing I'd consider another system.
cheers,
supervij