This may not count as a real find since it's on the Google's own support site, but this list of recommended IMAP client settings is interesting in that it differs from many of the Gmail IMAP how-to's I've seen so far.

Regarding Sent mail:

Do NOT save sent messages on the server. If your client is sending mail through Gmail's SMTP server, your sent messages will be automatically copied to the [Gmail]/Sent Mail folder.

...and Junk folders:

Do NOT enable your client's junk mail filters. Gmail's spam filters also work in your IMAP client, and we recommend turning off any additional anti-spam or junk mail filters within your client. Your client's filter will attempt to download and classify all of your existing messages, which may slow down your client until the process is complete.

I adjusted my Mail.app settings and noticed some marginal improvements. A big difference is that their advice for Trash results in archiving every single message in All Mail, whether you delete it from your client or not.