I use Lynx almost daily, mostly for reading HTML-Only email (I am shaking my fist at you, HTML only senders) and downloading things. Requiring J-Script makes me nuts.
I've got email accounts on a couple of servers I only access via SSH, so for them, mutt is a necessity.
Also, I use mutt on a couple of my machines so that I can quickly hammer through mailing lists and other not-quite-spam.
When using Gmail or Thunderbird, I use them in threaded/conversation mode, and I tend to process not-quite-spam in non-threaded mode.
Mutt is simply faster to hammer through that many single low-value mails at a glance (rather than other clients -- webmail or local -- that take noticeably longer to render the mail in preview mode).
Another benefit of mutt: I've got various F-keys configured to hop to different servers/email addresses. While GUI clients let me do that with several keypresses or mouse movements, none is as configurable to that extent as mutt.
If you have several online identities, these kinds of optimizations can shave hours per week compared to using a more fully-featured client. After all, unless you're a marketer (or have much affection for WYSIWIG word processing features), your emails are predominantly text anyway.
