Though the program is nearly perfect as is, I think adding a multi-line comment box would be a useful addition. To address your concerns, the tag panel allows one to optionally select which fields to include and exclude, and which to show as multi-line. Unfortunately comment is not one of them! But if it were added, then space would NOT be an issue, since it could default to single line, or to not showing, and the user could then change the setting in preferences to have it display in the tag panel (as multi-line, single-line, or not at all).
Alt-T is helpful for checking on one item, but for browsing through multiple items, it is a pain to press alt-T (or double-click) on every individual item, rather than just looking over at the comments box as you browse.
For many of us, there are severe limitations in the other tags available; for example, AAC/quicktime has no tag for performers, and does not allow multiple items on any field. Therefore comments is one place where a lot of that information can go.
The comments tag is unlike other tags since it is a catchall for user-designated information.
P.S. Multi-line should also be an option for title, since that can be quite long also. If I am not mistaken, I believe the options for tag panel excludes only the default fields from multi-line box option selection (i.e. they can't be removed so can't be "added" again to tag panel, so also can't be added as multi-line)--that may merely have been an oversight.
QUOTE (ohrenkino @ Jan 15 2011, 04:49)

Perhaps you may use the extended tags dialogue (press Alt-T) as a workaround for the time being.
A double-click on e.g. comment opens a freely resizable dialogue box.
(Yes, I have seen that your suggestion aims at the tag panel... but as the tag panel is rather packed with other additional information a larger comment box may spoil that purpose. And there are other fields like unsyncedlyrics, subtitle that could raise the same desires ... where should one stop ...?)