I want to change my all my blog comments links to Dofollow and attract more comments. I use good plugin for restrict spam comments and accept good comments only. It creates any problem in Google or other search engine.
As long as you keep those spam comment away from your blog you're doing good, there's no such rule in Google webmaster guidelines that blog comment should have nofollow attribute or else.
As long as you monitor your comments so your blog doesn't get spammed it can be very beneficial for your blog.
I would suggest having to approve all your comments before they're put up because you never know when these spammers choose to attack your blog. It's ok if you constantly moderate your comments to check for spam.
Akismet - Akismet checks your comments against the Akismet web service to see if they look like spam or not. Did You Pass Math? - Restricts comment spam by throwing the commenter a simple math question.
Good decision. By this way you can all increase traffic on your blog. I don't think there is any problem. You can use software. Google and other search engines only dislike black hat techniques.
i think this will increase ur backlinks too if some blogger wants to list ur blog on his do follow list
I actually just wrote an article on this over here: http://dofollowdir.com/articles/article-2.html There is one downfall that I've found: individual pages' PR 'bleeds' a lot more. i.e. you're getting what would be a PR2 split into 10 sites instead of just isolating it internally. But hey, PR is totally over-rated anyway. Seriously!
Traffic from Google SE reduced, I think Google penalize my site using Do follow. I add no follow once again. How to remove penalty from google
You are not penalized for changing comments to DoFollow - that's unheard of. If that were the case, sites like Digg would never rank anywhere in SERPs.