I do not feel the need for a fancy media player on my PC, I'll rather use iTunes, even if it looks a lot like a spreadsheet.
As probably many other people my age I do have a diverse music collection, featuring a lot of different songs from several periods and artists. And not just the latest fad on a high rotation playlist.
I use the iTunes rating system to manage my music library, giving 5 Stars to 1 Star ratings to organize my music:
5 Star -My hands down favorite songs I would not live without (currently about 100 of my 5000+ songs)
4 Star - Very good songs I would need on a flash based player
3-Star - Good Songs I do not need to hear everyday
2-Star - Songs I don't care much about but either are important music milestones or nice to hear once in a year
1-Star - Songs I need to delete from my collection
Unrated - Songs I need to rate according to the above scheme.
To rate my music I use a smart playlist called "unrated songs". When I'm on a trip I'll often access this playlist from my iPod and rate songs as they play. The idea is that I'll eventually rate all songs and then delete the 1 star songs out of my library.
Anyway, coming back to the title of this post: Beside using the iTunes rating I also store my ratings in the comment field within the MP3 (ID3) tags. For that I rate the music as usual and then use a smartlist which checks for all star rated songs not having a comment containing the word "star". Then I can easily insert the rating in the iTunes comment field (i.e. a five star rated gets the comment "5-Star"). This way I don't care if I loose the iTunes rating (or actually the XML file where it is contained) or my playlists - the ID3 tags do contain the rating itself so I can apply the iTunes rating again whenever I need it.
Since I lost my ratings once before, I'll rather store them within the MP3 itself.
By the way, for people wanting to export the iTunes playlists to other media players, there is always Eric Daugherty's fine app iTunes Export. And the great MusicBridge by James Willis if you want to copy/sync your meta data from iTunes to Windows Media Player (or the other way around), including transferring iTunes Ratings to WMP ratings.