Living in /mailnews/extensions/mailviews/, message views are a powerful tool to quickly filter messages of a particular folder, even virtual ones. With the advent of tags and their derived default views (Bug 349991 "tag mailview names out of sync with tags"), though, bugs/deficiencies in the message view frontend implementation are more visible then ever, see bug 201500 "Mailviews tracker" and bug 229537 "Make mailviews really useful as newsviews".
Bugs I'd like to fix now to finish the label → tag transition:
Bug 332802: View → Messages menu-item only visible when View (Mail Views) Toolbar is visible/present
This is a must-fix.
Bug 362990: Customize Message Views dialog's selection should not affect View menu selection
I agree this should be fixed, including making this "dialog" non-modal. In fact, at least for SM, this dialog should be a preferences panel.
Bug 362567: Customize Message Views modal dialog won't go away
Already has a simple fix, but will be irrelevant anyway if 362990 above is fixed.
Bug 199467: add ability to refresh current view
Easy, if we can just allow an already picked view be picked again, but this needs to be investigated (where would this cause problems, if at all?). See also bug 362741: Selecting folder with previous view unread, while viewing another unread folder, fails.
Bug 240921: MailViews don't apply to message changes
I don't think that automatically hiding eg. messages read in an unread view is a good thing, so 199467 fixed would make this WONTFIX.
Bug 362568: make it possible for frequently-used custom views to appear on View menu
Consensus seems to lean towards having just one flat list.
Bug 364542: View > Messages > All/Unread doesn't uncheck
Just a bug.
If there's a simple way to do it and if I have the time, I'd like to tackle these as well:
bug 116024: mail views & quick search leave the 3 pane window title as the message I selected
bug 135964: View → Messages Change Deselects Displayed Message
bug 191199: Message Views dialog should have Move Up/Down buttons
Most probably only as part of a pref panel.
bug 191485: Message view name should state "Untitled View <n>" by default
bug 191801: accesskeys don't work in Customize Message Views/Message View Setup