I was watching a TED talk this week from Luis von Ahn, the founder of CAPTCHA. Very interesting talk on mass collaboration over the web and how reCAPTCHA is allowing the web community to participate in a project to digitize books.
All very interesting, but what really got my attention was a new project that they're launching at the moment called Duolingo. It uses a similar approach of getting humans to type in captcha type words, but you're translating these words from a foreign language. von Ahn suggests this is an excellent way to learn a new language.
The site is still in beta at the moment and alas doesn't currently offer Czech as an option but it's certainly one I'll keep an eye out for. They have a video describing the service, which I've embed below for you.