I have a
SpotBot (pet model) that I absolutely love. You just add some water and cleaner, place the machine on the spot, push a button and then walk away! I use it more for dog messes but on occasion I'll find some bird poop that I missed cleaning immediately and it works wonders on it.
Plus side - does the work for you, you can control the amount of product used and you only use a little bit of cleaner to a lot of water.
Down side - only cleans one spot at a time. Might not be the best if you have a large area to clean. Also depending on your carpet having a really clean spot might make you realize how dirty the rest of the carpet it...
Edit Note: Sorry the posts got out of order, I deleted the original and reposted because I posted the url incorrectly.