I took some time off in the summer of 2007 and constructed a dedicated HT room for the family. Considering this was my first serious attempt at a renovation project, I am pleased by the way things have turned out.
The room is 21x15 with a relatively low ceiling which unfortunately did not allow for a tiered seating arrangement which is one my greatest regrets. There's a deep cavity behind the wall-unit so I built a bass trap behind the screen. A sub-panel was installed with 8 dedicated 20A lines for all the gear but unfortunately the light dimmers throw a lot of noise on the power line, but I felt it was a necessary evil for this room. Let me know if anyone has a better solution for dimmed lighting, but usually the lights are off during movies anyways.
I don't have ambitious audio priorities for this room, but would like to eventually get a processor with all the latest HD audio codecs. Something along the lines of the Cary Cinema 11a would be ideal but I'll wait until it is more mature.
Have to admit that most visitors are more intrigued by the HT room than the 2ch room including my own family. I only have one chair in the audio room anyways.