When implemented the correct way, profile links can be extremely valuable and effective - they're my primary method of linkbuilding. Here's how:
- High-PR forums (these have come to be known as "Angela and Paul style")
- Anchor text (the site allows anchor text)
- Double passing - register for the site, then come back a week later and drop the links in. This way, the attrition rate is much lower.
- Get them indexed. A few ways:
- Combine the links into RSS feeds and submit to RSS directories.
- Social bookmark the feeds and/or the links themselves
- Send more profile links to these profile links (known as a pyramid)
- Backlink Energizer (my favorite)
- some combination of these, and/or other methods.
The reason the usual "500k Super Ultra Spammy Blast Backlink Package!" idea/system/service doesn't work is that it lacks most or all of the things above.