According to BAA, now that Terminal 5 has opened, the other airlines are going to start a year-long process of moving to individual terminals for the different airline groups.

Terminal 5 will be completely British Airways.

Terminal 3 will become Oneworld (including a small number of BA flights)

Terminal 4 will become Skyteam (and unaffiliated airlines)

Terminal 1 will become Star Alliance (including Thai)

And all this is supposed to happen in the next 10 months. (October for UA - I'm assuming Thai will move at about the same time).

As for Terminal 2 - Planning permission to knock it down and replace it with a new terminal (Heathrow East) has been given, which Star Alliance will move into from Terminal 1 just in time for the Olympics in 2012 (supposedly). At which point Terminal 1 will be closed. (The new Heathrow East will replace both Terminals 1 and 2).

Oops - no they're not.

Star Alliance press release

It seems that Thai, Singapore and some others in the alliance aren't moving to Terminal 1, so Star Alliance won't all be under one roof until Heathrow East is ready in 2012 (if it's on time).

with all those problems with T5 there will be delays or even plans put on hold untill the situation gets under controll