A 302 redirect is commonly associated with doorway pages (or cloaked pages) where webmasters would create special pages designed for the search engines (which are usually laden with keywords and would rank high in the rankings) while serving up regular pages for visitors. The initial page is the page indexed by the search engine but when the site page is clicked on, it will redirect in less than half a second to the actual page. The lapse in time involved a switch-over from the page served for the search engines’ benefit to the page for the visitor. Google only bans the redirect site and not the target site. Thus, search engine spammers would typically use a throw-away domain that redirects to their money-generating site. While this worked for a while, Google has managed to overcome this difficulty while Yahoo still encounters problems with it.
There is possibly a sinister side to the 302 redirect or 302 page hijack. As Claus Schmidt explains it:
This exploit allows any webmaster to have his own “virtual pages” rank for terms that pages belonging to another webmaster used to rank for. Successfully employed, this technique will allow the offending webmaster (“the hijacker”) to displace the pages of the “target” in the Search Engine Results Pages (“SERPS”), and hence (a) cause search engine traffic to the target website to vanish, and/or (b) further redirect traffic to any other page of choice.
Find out how to spot Google hijacks and how you can handle them.
Again, we’d like to stress that use of unethical techniques to achieve rankings is frowned upon by the search engines and is not encouraged. There are ethical ways which won’t incur the wrath of the search engines or the community. You’ll find that you’ll sleep better at night knowing you contributed to the community and brought value to your visitors.