My disk performance is consistently bad.

Not sure what size Linode you're on–sounds like a 360. I think there's an I/O limiter. Perhaps you keep bumping into that limit, and need to upgrade based on your usage ;)

The disk performance seems good to me as long as I'm not untarring or compiling--but often these run very smoothly (on a 360).

I just bought an extra 360 for experimental stuff, and the I/O is fine. You shouldn't be bumping into issues- maybe it's the site you're running that's slowing it down? Is it just taking awhile to load a page?

Do you have any metrics to work with? I wouldn't be surprised if s single program was taking up more RAM or disk I/O than it should, and a fix was merely a tweak away.

If you're not running Munin, I highly recommend doing so. You can download it from http://munin.projects.linpro.no/, though it's probably available in a package for whatever distro you're running.

I'm on a Linode 1080, and the only time I run into any kind of slowdown related to disk access is when I'm doing really nutty stuff with parsing very, very large logs. Those tasks are something I really need to offload to another host anyhow, as it's better to do crunching like that on a separate host and just rsync the results back to the main host upon completion.

What sort of stuff are you doing with your node that appears to be causing high disk consumption? Perhaps there's a way we could help you find a way to reduce it :).