Comparison between nant and msbuild
You can find at this link, a table that compare nant tasks with msbuild tasks. If you look at this table it seems that msbuild lacks a lot of things, but actually there are specific visual studio tasks that have no equivalent in nant, like those one for tfs (open issue etc), publishing with clickonce, run a data generation plan and many more.
In the end msbuild is a great product, but probably it lacks a little on some basic tasks like XML manipulation with xmlpeek and xmlpoke.
Alk.