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The Browse mode only sorts by Genre, Artist or Album. You can sort on any other tag or field by clicking on the header for that column. Thus, you could select Blues in Browse's Genre window and then sort on Name, Artist, Album, Last Played, etc. You can also limit what is selected by using the Browse Bar by selecting Music, Audiobooks, Videos, etc., instead of All.
I use Grouping to add keywords so that I can refine conditions in Smart Playlists. Keywords might be a secondary (or third) genre, a region, other artists on the track, or what ever. I then can add a condition "Grouping contains [keyword]" to any smart playlist I am building. You could do something similar with the Comments tag.
None of my tracks have anything in the Category field and I do not believe this field can be edited by the user. I have not really investigated this field, but it may be used by videos or podcasts from the iTunes Music Store (I can't say for sure because I don't have any videos or podcasts). If you have any files with entries in the Category tag, you could sort on this field or you could use it in a condition for a smart playlist as well.
I use smart playlists a lot. They are very flexible and allow you to fine-tune your selection criteria and, with Live Updating, they are always up to date.
