I bought the Logitech Ultrathin keyboard based on the reviews that I saw on other sites. However, ever giving it a try for a couple of days, I returned it. The main reasons were (1) the cover won't fold around the backside of the iPad when you're not using it. Instead, it just comes apart and you have to set it aside and then reattach it later; and (2) the autocorrect feature doesn't work, but apparently this is a known issue with all Bluetooth keyboards. Even though the keys are fairly well spaced, it's still easy to make mistakes and it would be great to have the same autocorrect functionality as there is with the "built in" keyboard.
That being said, it's a reasonably well constructed product that typed well (but without autocorrect). If you're willing to deal with the drawbacks, go for it, but it's only getting two stars from me.