I went to a Montessori nursery as a child, and am now a qualified Montessori teacher.
The one thing I remember distinctly is coming home every day from college and telling DH about my day and what I'd learnt, and him saying, "That's just so LOGICAL".
Basically, if you can find a Montessori nursery that (a) can demonstrate how they implement the philosophy in the setting, and (b) have the actual Montessori equipment, then I think there'll be quite a lot of benefits.
Having said that, now that I'm a mum myself, my DS is in a "mainstream" nursery (mainly because there aren't any Montessoris in my area). However, he is old for his year (Nov baby) and at 3 years old, I can already see him outgrowing the nursery he's in. I think the activities there just aren't challenging (cars/puzzles/ironing boards/you get the picture).
Thankfully, there's a new MOntessori nursery opening near us this year, so I'll definitely be putting him in it when it opens - he just needs the challenge, and it fits well because he can work at his own pace and keep himself focused.
Wow, that was an essay!! 