yeah, this may not be meaningless, but I couldn't think of a better forum for it. if you haven't checked out project euler yet then you should. it provided me with problems to solve when I had no project. I solved about 50 of them. learned dynamic programming to solve one of them. now I am studying scala. once I get a laptop and install it, project euler would be a perfect place to go to learn to use it. I have java solutions for 50 of them. I think I should refrain from looking at them.
I heard about it a while ago - but never gave serious thought - as those problems are mostly mathematical - and usually do not test cleanliness of code and/or design (since solution is judged based on correctness and efficiency alone - usually 'good' solutions are very tightly coupled to problem statement and with very little scope to modify/extend).
But that apart, from pure mathematical coding point of view, those are very nice puzzle (and let me warn you - very additive! I just wanted to have a look at them a couple of days back - and before I knew I finished around 5 issues within half night ).
By the way, is there any such project/website to check code cleanliness or design principles (e.g. given a problem statement - can coder write a 'clean code', follow SOLID/TDD, can he/she identify which design pattern(s) would be most suitable for it - so that minimal changes would be needed for further requirements etc.)?