Another thing you can do on Facebook is hide content. For example, if all your friends are doing Farmville and you're sick of reading about how they got another pig, if you hover your mouse to the right of that posting a box will pop up that says "Hide." If you click it, it will give you the option to hide Farmville or to hide your friend. Click Farmville and you will not see anymore Farmville! It's great. I just want to see my friends' status updates, not all the games they're playing.
You can also hide friends (I've done this with some old HS friends who say some annoying things sometimes) and I believe groups you are a fan of. I think it's a better option than permanently deleting the friend.