[intadviser]

Widgets might be good as support in bringing extra-traffic, but quality posting and interacting with other bloggers, as jshaffstall is writing, should be in the core of blogging.

If there's spare space on blog, then I see no reason why not use them. As long as they integrate organically with the blog, and bring some free traffic, they do no bad.

Blogupp adds extra-visibility by giving credits for each visitor and is very simple. Some widgets give credits by visiting other blogs, like entercard does. Blogrush includes an affiliate scheme. Each of them have their pros, and the blogger itself should decide which one the best matches its need.