On dofollow versus nofollow versus allowing links or banning them

[Vekseid]

I've seen a few people put up questions like this, so, here's my experience.

Google takes Nofollow as a suggestion. Google has recently outright admitted this with regards to Twitter, but makes it clear that it is actually tracking user reputation in order to determine whether or not to follow someone's links. The threshold for this is not very high - I actually get juice from Twitter and I only have ninety followers.

This appears to be true as long as Google can attach the posting of a link to an identity of some sort - e.g. it can't do this on Wikipedia. Google can do this on forums, however, and if some member posts a link that you have nofollowed, and people are clicking on those links (which Google sees through its toolbar, say), Google may choose to follow that link.

For this reason, I have mostly abandoned Nofollow as an antispam solution, for several reasons.

1) Google's official answer is that 'bad neighborhoods' won't penalize you if you nofollow their links. But I have a feeling that with the rise of drive-by malware that won't necessarily care if it's nofollowed, this might not protect you forever.

2) Which forum would you rather participate in: One that is inundated with spam links but they are at least nofollowed, or one that has an active staff that prunes that crap to allow genuine discussion to take place?

3) Google seems to have a decent threshold and grace period between discovering a link to a bad neighborhood and penalizing you for it. This may get tighter as anti-spam measures improve, but we'll see.

4) Google likes it when you link out. Healthy, followed outbound links will not necessarily raise your pagerank, but they do noticeably help my search results. Giving credit, in general, is a good thing for the Web and I think that's what Google is aiming at, but that's just a guess.

So what should you do?

The anti-spam links modification can set a threshold for displaying links. This gives you or your staff time to pick out spammers.

The Stop Spammer modification can help prevent spammers from signing up to your site in the first place. This has the disadvantage that it relies on an external source, but for myself, it's been invaluable. Something like this could largely be replaced by placing registration bans on ASNs, bad MXes and Tor, if someone wants to make a more reliable version.

[seo_corporation]

Yeah,Yeah ..No-follow attribute of a link just means that Google will not pass the host's website page rank  to be passed onto the link but Google can certainly follow the link for indexing.
I am too getting value for my links on twitter which are No-follow . Not only twitter, Google follows links put on walls of Facebook too which are also No-follow. I was really surprised a lot when I saw one of my friend's website with a back-link ( counted by Google and shown with operator link:domain name) from Facebook profile. that back links is available still today. i am still confused how could this happen!! If you wish I can send you the domain for which google counts link from Facebook as back link.