I just organized my entire music collection into well tagged MP3 and M4A files and couldn't be happier; both iTunes and Sonos work better with clean metadata. The majority of my music comes from CDs which I'd ripped over the years. Between the crappy 128kbps MP3 of the earliest rips and the inconsistent metadata I decided to start over with a clean rip from a ripping service. I've also got some stuff bought or downloaded from various sources (mostly Amazon) with varying quality that I had to fit in. 1200 albums in all, 300GB.
A clean rip of the CDs was a great place to begin. I took all my discs to ReadyToPlay, a service down in Palo Alto. They aren't the cheapest (I paid $1.40/disc) but they came well recommended and their website does a good job explaining how they take extra care with metadata. I was really happy with the result of their work and enthusiastically recommend them.
ReadyToPlay's setup is a few robots loading discs into CD-ROM drives with dbPowerAmp doing the ripping and conversion. They ripped to Apple Lossless (m4a); now that Apple has opened the format it seems the best choice. ReadyToPlay licenses high quality metadata from All Music Guide and other sources so album and artist names are much more accurate than I've seen from free sources. They also do some hand editing and data entry as well as careful handling of the CDs and cases. Money well spent.
ReadyToPlay got me started with a metadata schema. Just 18 genres without silly micro classification. Artist vs. Album Artist vs. Composer is a headache, particularly with Classical music, but iTunes mostly does the right thing even if Sonos is a bit confusing. One clever thing ReadyToPlay did was stuff detailed genre info into the Grouping tag, so while Autechre shows up as "Electronic" in the basic Genre I can also find it in iTunes via a search for "Techno" or "IDM" or "Experimental".
I didn't really need to edit any of the ReadyToPlay metadata, it was correct from the start. The other music was more of a mess. I'm surprised at how poorly labelled Bleep and Amazon's early MP3 sales were. It took a few hours to collapse down the genres, fix up mislabeled album titles, and try to figure out what some of these unlabeled BBC Essential Mix tracks really were. But all that work is done and now I've got a great, easy to use music collection.
Anyone want to buy several boxes of used CDs?