[guelo]

If you hash it you can't determine the "strength" of the password except maybe looking up the hash in a rainbow table.

[mabbo]

Do your strength checks in javascript client-side, then hash, then send. Server side can do further checks if it wants on the hashed password (hey, this password was already used, etc).

[whiskeySix]

any clientside validation can easily be bypassed using something like fiddler.

[FabHK]

Password strength checking is (properly understood, in my view) providing help to the user, not enforcing some silly and annoying "password validation" rules.