I have a small doubt, i.e., How to identify the blog has no-follow attributes.

Either view the page source code for nofollow or download an seo toolbar that has "show nofollow" links built into it

SEO toolbar is the answer.

download a seo search status from seo book. a site that was shade of red show that sites are no follow site.

hi,
You can check follow & no follow by using SEO tool bar otherwise right click on web page and then check page source code of that particular web site.

Thanks for all the help. It was very helpful.

Thanks again

If you're not familiar with the donofollow addon on firefox, you can easily go to every post where the comment is present, press CTRL U , or view source, and then press CTRL F for find, and type in the word 'no-follow'. If it's there, there yoir comment id definitely in a no follow page.

Go to the selection source of that link and see in that whether no-follow is written or not...

just google for all dofollow blog so you won't have to check the source code of the blogs your commenting.

Many toolbar available in google just search with related keyword