I'd be grateful if someone can give me some problems or hints which will help me with testing and maybe improve further my thinking:) I'm talking about problems involving Quad trees, KD-trees, tries etc.

Thanks!

I suggest we do the same with the member photos. This is possible because unlike TopCoder, here you can change your photo instantly and the requirements for it aren't that strict (for example see rng_58's). I imagine how every one or two months on a specific number of the month there is a certain question or theme and everyone has to change his/her photo (for a couple of days) as an answer to it. 

Let's say the question is "What's your favourite food?" and everyone has to upload a photo of his favourite food. Well, I guess most of the photos would be some kind of stakes then. Some other questions like "What is the most beautiful place you have ever been to?" will be quite interesting also.

Do you like the idea? It will be fun for sure:)