I don't understand why people throw up 20 links on one page. What a waste! Every link you add divides the amount of link juice that is available on that page, dilluding the amount of authority that the site you are promoting with the link gets!

I only put a max of two links on any page when link building. Aside from flying below the radar it means that each link is worth more. If you need to promote a lot of sites, you need to create different accounts and spread it out.

Another problem is co-citation. When you put multiple outbound links on a page all to untrusted sites, it casts a shadow on all the link on that page. If I ever DO put a third link on a page I point it at an authority site in the same niche (one that is not in the top 10 for the particular search term I'm targeting...don't want to juice up my competition after all). This way co-citation works in my favor.

I guess people don't DO things the wrong way link this because they are lazy...but then they get frustrated when they don't get the results they want.

Commenting in forums is always risky.

Even if you write a great comment, the links in the sig file are a dead giveaway.

When looking for forums to get backlinks from, check if the profile is publicly viewable or not (often the webmaster will disable it) so that you don't have to comment and have a better chance of staying under the proverbial radar.