In school gangs were generally not such a hot idea. They tended to use the strength of the amassed group to bully and generally help the ring leaders get their own way.

Fortunately not everything is like school and joining a group of like mined individuals is, these days, far more focused on working as a group than pulling down others. This group membership can help you to promote your site by building a shared relationship with people likely to be interested in your site.

Such group activities as Spike Club and other Blog Carnival's are a good way to both socialize and co-operate with other sites (especially blogs and journals) in your topic field.

A Blog Carnival is a type of blog event. It is similar to a magazine, in that it is dedicated to a particular topic, and is published on a regular schedule, often weekly or monthly. Each edition of a blog carnival is in the form of a blog article that contains permalinks links to other blog articles on the particular topic.

There are many variations, but typically, someone who wants to organize a carnival posts details of the theme or topic to their blog, and asks readers to submit relevant articles for inclusion in an upcoming edition. The host then collects links to these submissions, edits and annotates them (often in very creative ways), and publishes the resulting round-up to his or her blog.

Many carnivals have a home page or principal organizer, who lines up guest bloggers to host each edition. This means that the carnival travels, appearing on a different blog each time.
From: http://en.wikipedia.org/wiki/Blog_Carnival

It is worth noting that this form of promotion requires both active participation and a suitable site already matured into it's topic (and not created yesterday at midnight after lots of beers because you felt it might be a "cool idea").

This is because of a fundamental truth to site promotion - no mater how smart you work, you must still work. However, by joining in with activities suitable to your website and it's topics (even if this does co-promote sometime rivals) you will gain significant returns from the time and effort you put in. Returns not just in traffic and increased visitor rates but in the general satisfaction that comes from being part of something bigger.


Notes: More Details on blog carnivals can be found at the link you just skimmed past. Spike Club is not a simple carnival but should be good fun nevertheless.