I am concerned that it is forbidden even to question Haskell advocacy around here, even where it extends into pretty bald bashing of other languages.
In fact, this is so useful that new versions of GHC are going to support "type holes". If you don't know what type you need in any particular part of the code, you can just write a _ there, and the compiler will tell you what type goes there! So really, you're not spending time telling the type system which assertions to make--the type system is telling you what you need.
This is going to enable a much more interactive development style that leverages the power of the compiler to help you write your program. I think a more interactive development system is the future, and this is a good (albeit fairly small) step in that direction.
Also, as an interesting aside, the type inference can actually make your code more expressive. In both Haskell and Python, you could write a function called toString that takes an argument and returns it as a string. However, the really cool thing is that in Haskell you can write the opposite function--fromString. This function takes a string and returns a value. The real beauty is that the compiler can infer what type you need and choose the appropriate parser; in Python (or, really, virtually any other language), you would have to specify whether you want an int or a double or a Foo or a Bar explicitly.
So: the types are inferred for you, you can use these inferred types to help you write your program and they actually make the code more expressive. I think it's a pretty good deal.