My son is 3 in November and has only really started talking in the last month. Before that he had some noises, some signs he had invented and about 8 consistant recognisable(ish) words. I am pretty sure there is nothing wrong with his hearing, and in every other respect his development has been similar to other kids his age. He has seemed to understand everything I say to him for ages and also has always been a very happy boy so I wasn't too worried.
Everyone I talked to said the words would appear eventually, and he'd 'suddenly start talking and I wouldn't be able to shut him up'. I didn't believe them, but he's babbling away now - his words aren't as clear as some kids yet, but he's trying to say everything and putting sentances together. He seems to want to talk now, he didn't seem to want or need to before.
The only change in his life recently has been he started pre-school 2 months ago - he does 2 mornings a week. I don't know that the sudden talking has anything to do with this, but I wonder if being with people who can't interpret every noise of gesture and respond in the way that he wants has pushed him into communicating.