DD is 28 months. She doesn't really tell us when she's done a wee or a poo, although often seems to know she's about to wee as she stops and sort of looks down! She's a bit hit and miss if we ask her whether she has been too.
We have a couple of potty's (courtesy of MIL for her 2nd birthday 
), and I think she knows what they are for... sometimes she likes to get one and take her trousers and nappy off and have a sit, but never does anything. She also says things like 'do a wee wee on potty. She regularly has nappy free time anyway, however I find she will hold in a wee until her nappy is back on more and more.
DC2 due in early August, and DD will be home all summer as she's in term time only childcare. Part of me thinks we should try and train her over the summer when we are all home (DH is a teacher) but I don't really know if she's a) ready, or b) having a new baby added to the mix will be unsettling and make it a disaster. There is no rush but having the summer seemed as good a time as any!?