After trying MW 6.0 for a bit, here are my suggestions to further improve this excellent product:

1. More customizable toolbar (selectively adding other functions from the menus) and option for text labels to the right of small icons.
   
2. When processing mail, minimizing, and calling mail client, add option to add a command to the mail client (to send/receive in Outlook, for example, with F9).
   
3. Ability to set display font and size in MW windows.
   
4. Export and import settings
   
5. Make the error triangle icon either bigger, on the left of the window, more prominent and/or flashing. I too often miss it.
   
6. If an email is hidden because it is marked spam by a user rule, it can be marked good by the learning filter. Unless hidden emails are reviewed and corrected, I suspect the learning filter is contaminated by this bad emails it is learning as good. It seems this phenomenon is a weak point in design. Hiding mail with defined rules that you are very confident is spam is a good feature. There should be an option to have the learning filter bypassed if the mail is to be hidden or at least for each defined rule. Alternatively, the learning filter could be one of the filters in the list and could be put somewhere in the filter order with filtering stopped when a definite classification is made. Then, if a mail is classified by a user defined filter, further filtering would stop and it wouldn't reach the learning filter if it was placed below the user defined one. Spamhilator works that way (also Outlook rules) and that system works well and offers more user control.
   
7. And clearly the biggest one: a better rules editor with more ready reference to syntax and capability to organize rules and statements between rules.