I don't think I'd want to make general pronouncements, but our experience was that DS was in nursery nominally full time from 10 months until he went to school. In practice DH and I had flexible hours and he'd be there typically there 10-4ish, less to start with. He took a few weeks to settle in, but after that he loved it almost always, and still talks fondly of it (at 8). Of course I don't know how he'd have been without it, but my intuition is that it helped him hugely with forming relationships and generally interacting both with other adults and with other children. I think we were lucky with the nursery: they had very low staff turnover, so he formed real relationships with the staff, most of whom were impressive; the nursery was attached to the university where we work, and so I think "gifted enriched"; and they made almost no attempt to do academic things with the children, so his being ahead there was never an issue. They were age-sorted inside, but they all played together in the garden a lot, and he often played with older children there. Indeed, the worst fit was the last year, when he was one of the oldest children there. He was a late talker, so he never experienced the frustration of trying to hold conversations with completely non-talking kids. If I have to put my finger on one major benefit, I'd say that it was that he got plenty of practice in *not* always being the centre of attention, instantly responded to etc. - he's very good at self-entertaining and fitting in (much better than either parent at the latter ;-), and I credit nursery for starting him off on that path.
