I've been having this problem for the last few days too - its just my rear right brake though...
Ages ago, shortly after I got my starlet, i had problems with all 4 brakes getting excessively hot (but the back right was the worst) until it wouldnt physically move and i had to wait 20 minutes for them to cool down until I could drive it again..... also warped my discs to fcuk
then I got told by a mechanic that the handbrake ratchet in the rear-right caliper had seized, so replaced it with a 2nd hand one I bought off someone on here, and until now I've had no problems
This morning, i left my house and then like 2 mins later my rear-right wheel just started skidding down the road past all the mums walkin their kids to school, I must have looked like a right twat lol!!!
Anybody got any ideas? I don't like driving my car like this - can't help thinkin that if i take a corner and the brake decides to lock on then im gonna spin out into a 3 tonne 4x4 coming the other way!