"Hey, A Link Is Still A Link, No Matter Where It Comes From, Right?"
Wrong! This is a misconception that can easily get you in trouble. This approach could bring you short-term benefits 2 or 3 years ago, but major search engines (especially Google) have gotten a lot smarter since then.
If you still think theme relevancy is nice-to-have rather than a must-have, well, think again. Get a hundred unrelated links pointing to your site, and several things will happen, none of which involves high rankings for you:
* Google will simply not count these links when computing your ranking. This is the best thing that could happen since it doesn't involve penalizing your site;
* Google will think (justifiably) that your site belongs to a different theme (say, gambling) and treat it accordingly....