Yes, our dd is in Reception and able, but I have no idea if she is on the register because I haven't asked!
As for your other question, we realised she was bright when she was 2 - that was when strangers started to comment on her language skills, and when she learned a her letters, numbers, colours etc. She was also swimming front crawl before she was 3 and still loves swimming. She taught herself to read when she was 3 - mostly from signs - pre-school used to have a 'letter of the week' and tell the children what sound it made, and she remembered them and put them together spontaneously. She's not extraordinarily clever (I have read about various children who were reading fluently and speaking several languages by the age of two, for example, and she couldn't do that!)but last year her keyworker at pre-school told us she was the brightest child there. Like one of the other posters' children, is really interested and suited to reading,writing and maths skills. She's in a mixed age class (Year 1s born after Christmas, and Year Rs born before Christmas) and has just been moved into a good Y1 reading group and goes up to Y2 for phonics. Her little Reception group are bright, so they all do the Y1 maths with the older ones. She's a lovely child and enjoys drawing, writing, playing board games, riding her bike, Lego and lots of other normal 5 year old activities, but also tries to write her own jokes and poems, does Sudoku, picks out famous tunes on the piano by ear (one finger!) and has an incredibly detailed understanding of the public transport system, traffic lights and road signs! 
I actually think she is a bit of a boring academic (in the nicest possible way!) but she has an outgoing personality too, and we've had trouble with her bossing the others around, always wanting to win, to be first in every line, etc. She is also pretty uncoordinated - I think that's hereditary! I was in two minds as to whether to mention her abities to her school, and in the end, I didn't.