To update.
When I first installed iOS 4, I immediately used redsn0w to enable background pictures, multitasking, and install Cydia.
That was a mistake. It was slow and crash-prone. None of the Cydia apps worked, and neither did iBooks! The app worked fine, but I couldn't download any books, they would claim to download, get to 100%, then sit there, with the download bar still visible. The books would sync to my computer, but a "loaded" book back in the iBooks app would disappear, and I'd have to redownload, only to see the same thing happen. Plus my battery life dropped like a rock.
So I went back to a stock iOS 4. Pretty bland, really. Not much difference from iPhone OS 3. I do greatly appreciate the single Mail Inbox, though. I have 5 email accounts, and having all of their inboxes together is wonderful. And while folders are nice, they're not a make-or-break kind of thing.
And while background pictures are nice, apparently they are the performance drain and battery killer. Some sources claim that iOS 4 uses the GPU a lot for rendering the wallpaper, and the 3G's GPU isn't quite up to the task.
Multitasking, though, is nice. I did miss a customizable double-click; but being able to stream Pandora, or use other multitasking functions would be very welcome. And while I was actually having the background process running, other apps were perfectly responsive. It was only the main home screen interface that became slow. And that may have just been the wallpaper slowing it down.
So I'm now re-redsn0wing, this time JUST adding multitasking. No wallpaper, no Cydia.