Let me start off by saying that I love the way Media Center lets me tag my videos without changing my video files in any way. So far the only other program I've used that does that is iTunes, and it's support for video is ridiculously limited.
I keep a lot of home videos (upwards of a thousand) and being able to tag them is extremely handy when I'm looking for something specific. It would be nice, though, if there were a way for me to add multiple values under one tag.
For instance, I organize my videos using the Series tag, with names like Spring Break '02, Summer '03, Christmas '05, etc. But I also use tags like Jersey Shore, Adirondack Mountains, Vermont Ski Trips, etc. Because of this, some videos may fall under multiple categories (i.e. Jersey Shore and Summer '02). As far as I can see, it's impossible for me to have that one video listed under two tags unless I make two physical copies of that video.
If I overlooked something that is already available to me (believe me it's happened before) then just ignore this post. Otherwise, it would be nice to see this, or something similar, implemented in future releases.
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One other small change that would be nice is the ability to resize the top panels in "Pane" mode. When I have Year displayed up there, I don't need it taking up 25% of the screen width for 4 characters.