care to elaborate?

Haskell is the only widely used language that uses lazy evaluation by default. This has historically lead to confusion and difficulties with reasoning about time and space, particularly when a programmer is coming from a strict language.

Why do we care about laziness by default? Like purity, it adds power and expressiveness.

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Finally, what would a strict Haskell be like? Here's a discussion: http://augustss.blogspot.com/2011/05/more-points-for-lazy-ev... )

Space leaks.

Also, unpredictable program behavior (which nearly destroys its usefulness in embedded beyond what perhaps Galois has been doing).

For what is worth, Edward Yang is writing an excellent series on space leaks in Haskell:

http://blog.ezyang.com/2011/05/space-leak-zoo/

The series require Haskell knowledge but this summary is fairly readable if you have a good grounding on programming language theory and implementation.