They have a huge problem with filters and small (iBook) screens. If you set up a filter with 20 items (the maximum, at least it used to be), you can't see all the options on the bottom of the screen. Basically I can't change the options on what to do with an email when this is the case (maybe they're trying to tell me something?)

Also, they still haven't (up to the last time I noticed) fixed a bug I have downloading attachments to mail. Downloading through my DSL, it seems that PowerMail almost locks up (doesn't accept many of the events I'm attempting, clicking on mails etc) when its downloading a large attachment. When dialing in through a modem, everything is fine. I can do other tasks while its downloading.