High cashback, but long wait
I upgraded to FTTC in September to take advantage of a £90 cashback offer. The upgrade didn't track, so i had to manually raise it. This meant that the cashback took about 6 months to come through. I cant say if this is particularly slow as the upgrades part of TalkTalk cashback hasn't been around to long.
I am happy that I received £90 cashback when the monthly cost is £10 extra over standard broadband. That's 9 months free!