View the pages source code and use CTRL+F to search for the word nofollow in the code. If you any piece of code that looks like rel="nofollow"; the blog is almost certainly a nofollow blog. If none of the links provided by the blog include a nofollow parameter, then the blog is probably dofollow.
you can download this ad ons that will able you to see if certain sites uses no follow or not here http://www.quirk.biz/searchstatus/
Actually since were on the topic here. In my sig the link The Groovytastic Blog Digger is a fantastic new tool that only seeks out blogs the "DO NOT" carry and use the "no follow" attribute. It's very handy, and it finds you very targeted blogs to be posting on, because it seeks out blogs based on keyword input. I'm totally glad I latched on to it, it's just one of those amazing must have tools in your arsenal. Cheers and hope that helps, Davin
typically, I look for a post that already has a comment. Goto the page with comments on it and find as unique a link text from a comment as I can find. Right click on the page and click view source. Hit Control F (in firefox) this will make a small text box in the footer of the browser. Type the unique text, which will show you the link tag if you find rel="noFollow" then it is a nofollow. Rel="external" is fine, that just makes the link show up in a new window. it normally takes me about 10-15 seconds to check a page this way