You can use them, but they are not that much of effecting compare to other link building process. you have to be assure that you not spamming of them. their moderation panel is too high. some silly mistake and your id get banned.
Good advice, and instead of just spamming, you can help prove your authority/experience and build up a rep similar as you would on forums. It can be worthwhile depending on your experience and your industry. From what I know, very few links on Answers are regular links and most are nofollowed. Can't say I know first-hand on Y & G groups as far as nofollow goes but I would be shocked if either wasn't employing them.
yahoo and google group can be used.. though seoviviti and brad callen were right..you have to be careful on posting or the moderators of the group would find you spamming and banned you..
I am new bie in im i tried to make links but when i checked it shows zero can anybody tell me the reason?