i changed my blog comments to search engine friendly. removed rel='nofollow' Code (markup): from expr:href='data:comment.authorUrl' rel='nofollow' Code (markup): now a comment can get a backlink fro my blog. But i wanna know Does it have a bad effect on Seo
Now you will have to keep your commentators home page addresses, because they often write 'http://none' etc. And as I know, incorrect links isn't good.
Remember, the less outbound links you have the more pagerank juice you spread to your outbound and inbound links. I personally would use nofollow in your blog comments, other wise your wasting pagerank and bringing on spam trouble.
It should not be a problem for now other than those spammy comments who wanted some search engine juice out of your comment section. However, since Google has already taken off the "Your Link" space from Blogger comment system, it is widely speculated that Google might be targeting blogs with dofollow comment section. I have wrote about this at Ending Do-Follow for Google.
By default the comments on the wordpress blog is no-follow. So since u have removed the no-follow, now u need to get install a comment plugin like Spam Karma on your Blog.
if you r using Blogger (blogspot) the go to template> edit html then check mark widgets expanded And find expr:href='data:comment.authorUrl' rel='nofollow' Code (markup): and remove Remove This rel='nofollow'