I did the first 100 in about 10 minutes and part of those 10 minutes was used to fast forward through tv commercials. I did the last 100 levels in about 20 minutes. Altogether there are 1200 puzzles.
If you like this genre, definitely try the harder games listed below.
Similar games (this list is incomplete):
Movez Pretty much the same as Block Mania but it has 1680 levels. I've solved 592 of them. That's probably enough.
Frozen Ice Cubes What's different: there's a point of 'no return'.
Escapology, reviewed by Nicola Salmoria. He told me about this game ages ago. I played it and enjoyed it, but never blogged about it.
Block Mania Similar to Movez
Move Puzzle - A Funny Strategy Game, Matching Tiles Within Finite Moves
Vubu What's different: the vubu men have different powers. Very sophisticated, very intelligent. Possibly the very best in this genre.
Move: A Brain Shifting Game