No, I don't. Why block them? Take Yandex as an example which is a Russian search engine. Even if your website is not aimed at Russians, it is still good to get more traffic from the search engine and there are uses for bots so I think generally it is a bad idea to block bots.
I wouldn't block them. 😛 That would be bad for SEO, because the crawler bots are what analyze your content. Without them, your SEO wouldn't be very good at all.