I didn't see this covered in any of the reviews of the iPhone 2.2 software but I'm really excited that they really smoothed out the process of updating applications that you've installed. The first great thing is that the "Update All" button has reappeared, and with 2.2 it actually works. I've updated as many as five applications in one swoop and had zero problems, including some big applications.
The other great touch is that you no longer get the new version installing in another window, and then jumping once the old version is out of the way. It now occurs "in place" where the current application is. It's a small thing, but really makes the updating process feel solid.