Apple had just released itunes plus which has two main benefits, both are great.
1. All the songs are now going to be DRM free, so you can play them with different software and players.
2. The bitrate has now doubled so that the music is better quality. (I suggested the itunes bitrate was too low here, and how to get round it, but now apple have ‘fixed’ it for downloaded songs.)
There is a great feature on the itunes store home page that will automatically (for a fee) upgrade all your songs!
To find it you go to ‘quick links’ on the right, and click on ‘Upgrade my Library’.
It will give you the option of deleting your old library or moving it to the desktop. I suggest you keep it, because if you ever need the lower quality 128 kbps songs (eg to listen to on your ipod), the original downloaded ones will be better quality than if you re-compress the new 256kbps down to 128.
Thankfully I have only purchased 20 songs from itunes, so the fee was just $10.