Google's cache only last a handful of days. It's very useful if the Website is down temporarily (for maintenance or overload for example) but totally useless otherwise.
Kind Regards, Dodoïste
2010/8/24 theo10011 de10011@gmail.com
Its a great idea, using the wayback machine to ward of link rot. I support it but doesn't Google cache offer a similar service. there is also deadURL.com which uses Google Cache, the Internet Archive, and user submissions for gathering dead links.
I would guess that Google Cache would have the highest and the longest reliability, at least as long as Google exists, its their business.
Regards
Theo