Web Caching - do you use it on your site?

I came across a useful tool, which probably explains the META cache="30 days" etc., that I've seen on some sites. Although, I've noticed Google and Yahoo don't use it.

Here's the link:

http://www.ircache.net/cgi-bin/cacheability.py?

It is useful to use cache on your site?

 

It is on those META tags that I do not use. Most SEs and every browsers do not pay any attention to it

 

That's what I thought, but when I checked my site with the link above it made me wonder...