yes nofollow links also usefull as well as dofollow because if user click on that link then link will be good impect.
Some would say that it would not help pagerank however I have read that it is not 100% clear how google treats no follow and that it still factors it in.
it's to my knowledge that no-follow backlinks aren't worth your time because google can't track back to your site.
Nofollow links are very important. If you only have dofollow links it will look as if you have paid for them or that you are trying to manipulate the search results. Googles favourite word is natural. Link with a mix of PR levels, nofollow and dofollow.