I love the T3 lounges and most of my s/h flights are from there (VIE, BUD, PRG).
The fact that you can lounge hop between AA/CX/BA and try it all is great, and when I soon get my Gold I will be on cloud above all others ;-). Pity that most BA FTers depart from T5 and I rarely get to meet-up in the lounges with you guys!
PS: Also how close everything is and that you don't have to take a train/walkways to get to some annex/satellite is very much appreciated.