If the OP is keeping the same line and number etc . there is no specific reason it should get messy - yes some people have problems but the VAST majority of transfers do go ok.
I've never heard of one ISP buying out the contract of a new customer - just won't happen.
TalkTalk don't have the best reputation (but it is getting better), but a lot of the problems do seem to stem from their telephone support centres. And yes they are overseas. But there are ways round that to get UK technical support if you have problems.
I'm a happy TalkTalk customer and would recommend them to anyone - but if you're a happy PlusNet customer I would strongly advise that you talk to them first and tell them you are thinking of leaving - and I wouldn't be at all surprised if they matched the offer.
But if you don't ask - you will never know.
Edited by deleted (Thu 18-Apr-13 10:11:55)