This is great for working offline, and it also means that the docs are always usign sdoc, which is a great template which allows for good searching. >90% of projects have crap rdoc templates.
I do agree that building ri is a waste of time, though.
If you install your gems without rdoc on, you can just use open_gem (http://github.com/adamsanderson/open_gem) to build the rdocs on the fly with `gem read <gemname>`
Being a sysadmin (who did a lot of gem installs on production for the devs) rather than a Ruby guy, I didn't know this was a tip. I always figured everyone wanted this stuff, and I was the odd one out. Besides, no one should be reading rdoc on the production machines anyway.
Great tip. I sometimes remember to add these while I'm typing gem install..., but most of the time I forget, so this will help.