FBReader is now using tags to catalog ebooks. This allows the same book to appear multiple times under different categories. It automatically imports all <dc:Subject> metadata entries from OEB and MOBI ebooks and <genre> entries from FB2 ebooks. MobiPocket Desktop Reader can't handle multiple tags, but it does have a Genre sort option.
MobiPocket has a standard list of "Main Subject" options which is a drop-down list in the Publisher's edition of MobiPocket Creator, but is also on its All Categories
page. These are what get displayed as the "Genre". One of these may already be embedded in some of the MOBI e-books available here for download. It would be best for all relevant MobileRead tags to be included as <dc:Subject> entries in MOBI e-books, and perhaps this could be automated.