I was just there yesterday. The Sky Team lounge in T4 is between gate 21 and Starbucks. It is very nice, quiet, well furnished (with plenty of seats), with much better food and drink selection than the Holideck (which was tired-looking and noisy when I was there in May).
Seems like I read something on this board somewhere about Continental making a deal to keep their access to the ST lounge for another year or so. ??

Also -- there is a large sign posted in the gate area saying Sky Team airlines are moving into T4 as of November 1. I kind of wish they wouldn't do that. My last several trips into/out of LHR have been pretty pleasant, with nearly NO lines at immigration/passport control, and very short security lines. It just doesn't seem as teeming with humanity as T5 and other terminals...