host51 thrashing?

I have a Linode 256 on host51 in Dallas. This is pre-upgrade, and it will presumably become a Linode 512 soon.

I only use this server for personal email (IMAP), plus a lightly used web server. But, I'm starting to see performance problems on a regular basis: Typically, my IMAP client becomes slow to respond.

If I SSH into the server and run top, I see the CPU with very high "wait" percentages. I think this is I/O wait.

But, when I check /proc/io_status, I have plenty of tokens and there's no indication that I'm doing any significant amount of I/O anyway.

Is someone else thrashing the server?