Hi Bumper. I have a little experience with both nursery and childminder, but much more with the former. We opted for a nursery mainly because we had no personal recommendations for a childminder, and I wasn't prepared to leave DD in someone's home with no oversight.
Having used a friend's childminder to fill in some gaps when DD was a little older, I saw a few other advantages of nursery, mainly not relying on a single person to provide care. The childminder had some health and personal problems which left my friend in the lurch on occasion, plus having a school-age DS she took leave in school holidays, hence my friend had to do the same before she actually needed to (ie when her DD started school).
On the plus side, now that my friend's DD is at school, the childminder does some of the school runs, leaving my friend better able to work (she has two younger DCs, and the school/nursery combo seems like a nightmare).
Contrary to Pavlov's experience, nursery has been very inflexible for us, as they are extremely popular and the only way you get an extra session temporarily is if someone has taken their child out to go on holiday, and to change permanently takes months of notice. The childminder was far more flexible, taking DD when I went on courses and couldn't get a session at nursery.
The big advantage of having been to nursery (and this would be the same if a child was with a childminder but also a more conventional preschool setting) is that DD has acquired lots of essential skills for school - not reading and writing, but sitting still, listening, lining up, taking turns, asking to go to the loo, etc.
Finally - vouchers. You don't get them, the preschool setting (nursery, childminder, preschool) gets the funding. They kick in the term after DD turns 3 - she's a summer baby, isn't she, so it'll be September 2010? You declare what settings she is in, and depending on that the nursery/childminder would either get the full amount (two session's worth, if she was just in for a day) or it would be split with the other setting(s). Oh, and don't forget work do salary sacrifice for childcare, will save you a bit of money.