Ask HN: Opinions on Codechef/interviewstreet/codeeval/etc?

Hi, so I recently joined some of these websites and tried out some of the questions. At the moment I think that solving these things while reading through an algorithms text (I'm using CLR atm) may be helpful for...well, algorithm knowledge in general.

Some questions:

-How true is the aforementioned statement?

-What do you think about how sometimes these problems act as things for recruiters to look at?

-Any other thoughts?

I feel like these questions are not "practical" questions but getting an okay implementation is maybe a passive skill useful for coding in general.