A while ago, i asked the guys from Unity Application Block, about the commercial use of this library. Here´s what they say
I am not a lawyer. Licensing is
fundamentally a legal question, not a
technical question. And you cannot
trust anything from a lawyer that
you're not paying. So if you're
betting a business on this (or any
other library / software), get an
attorney to look at the license and
give you an actual legal opinion.
Having said that, the intention is for
the code & binaries to be usable in
whatever way you like. Take just the
binaries you want, and distribute them
however you like. You can also
distribute the source code, or even
make changes to it and distribute
them. What you cannot do:
1) Claim that you wrote it.
2) Remove copyright notices on the
current source files or binaries
(which are in the binary's resources).
3) Sue anyone over patent infringement
in the Unity software and continue to
use it.
4) Edit the source code and release it
under a different (well, incompatible)
license. The upshot of this is you
can't take the unity source and
re-release it under GPL.
5) Your software's license must be
compatible with Ms-PL as far as
redistribution of Unity is concerned.
Commercial licenses are fine.
I think that's about it. It's an OSI
approved open source license, and is
about as free as you can get.
Again, though, if you're actually
concerned, get an attorney, don't
listen to an engineer. The law doesn't
make anywhere near enough sense for an
engineer to understand. ;-)