My husband and I spent a day and a half at Keoladeo (24th & 25th December 2011)
We had a brilliant guide and saw 110 species of birds in that time.
Lots of beautiful owls and raptors.
I would recommend hiring a naturalist if you're not familiar with Indian birds as we would have spent time trying to (unsuccessfully) identify them and would have wasted most of the day.
Our naturalist was able to identify most of the ones we saw by their call. (In fact the only ones he couldn't ID by tehir call were the ones which were quiet!) The other added bonus was that he knew the places where lots of the owls etc roosted in the day.
I'd highly recommend the reserve even if you're not a birder, it was nice to escape the hustle and bustle of busy everyday life for a few quiet hours.
If anyone would like the contact details for the naturalist we used, I'd happily pass them on.