When it comes to blackhat techniques to improve seo, the linkwheel was one of the most popular.
Linkwheels were basically a collection of web properties which linked to each and to your target page. Blackhat seo involved creating a set of web 2.0 properties, each linking to the next and to the page to be promoted.
After the Google Panda update, a lot of the link juice from linkwheels was nullified. Google figured out an easy algorithmic method of identifying link wheels and link juice from such setups were de-emphasized. This did not stop blackhatters from continuing to sell linkwheel services. This would go to show that although effect is minimal, it still exists.
There is now however a whitehat approach to making use of the link wheel concept. Googles focus was to kill any link juice passed from web 2.0 property based linkwheels or from sites that only existed for the purpose of a being a spoke in a linkwheel. The new approach is to use legitimate links to generate each of the spokes of the wheel.
For example, a guest blog post could credit another element in the linkwheel rather than linking directly to your main site. That next element would link to another property and so on and so forth until the final page which links to your target page. The primary benefit here is that the final page which links to your site would get additional link juice from all the other links that lead to it.