Tried using Genre/Rating to create Smart Playlists but found this too hit an miss (too many crossover artists in my collection perhaps)
Instead I have added comments as follows:
Radio 2 (Easy listening, oldies, etc)
Friday Rock Show (Hard Rock, Metal etc.)
XFM (Alternative, Pop-Rock etc)
Jazz FM (Blues, Jazz etc)
A track can have more than one comment and fit into more than 1 Playlist!
Now I can set a Smart Playlist:
Comments contain XFM, Rating is greater than 2 stars
This crosses genres and gets that obscure Captain Beefheart and Zappa tracks in amongst all the Alt. Rock, Pop Rock stuff. I can have an Eagles track along with my Metalica if I feel that way inclined.
Once all tracks have relevant comments I only have to rate them on the fly and they are added to Playlists.