But, there's a catch... [d'oh!]

It's only available for the Navigation Edition. ** EDIT: It's now out for 0577454 **
So... if you have the good ol' XpressMusic you are SOL for the moment. However, you could follow my instructions in the How To section on changing your product code to the Navigation Edition and get the update now.
Nokia 5800 XpressMusic NAM/US type RM-428 product code 0577454
Nokia 5800 Navi Edition NAM/US type RM-428 product code 0591814
Currently only available through NSU (no FOTA yet).
This new firmware incorporates the home screen from the 5530 with the scrolling contacts bar widget so you can have more than 4 contacts on the home screen (I think the max is 20 now). however, the size of the contacts bar has increased so only 3 show on screen at a time (vs 4 on the older firmware).
Also, it is now possible to have both the contacts bar and shortcuts on the screen at the same time.
Kinetic scrolling has been added, but still doesn't work in the web browser.

Overall performance is good. Screen response and phone speed seem comparable, and maybe even a little better than v31.
Web browser stability has improved (better than v31 but is still not as good as it was with v21). Flash support is still at v9.1.121.31 (same as v31, or older firmware with the Flash Lite 3.1 update).
Ovi Contacts is included in firmware (but the original contacts app is there as well).
Oh, and text input will automatically switch between T9 in portrait mode to full-screen QWERTY in landscape mode (this is really nice IMO).
While the new Contacts home screen looks good, there are some issues


With the older contacts bar I could have up to 5 people only 2 taps away. 4 on the contacts bar (just tap the contact, then tap the phone icon or green button), and one at the top of my contacts list (put a "1" in front of their name to sort them there).
Well now only 3 are on screen, and when you tap one and then tap the phone icon or green button it will ask you if you want to dial the mobile or home number (instead of defaulting to the first number like before). So now it is at least one additional step (+ scrolling if needed).
With the old contacts screen you could also start a new text message with only 2 taps. Now it's not only worse, but it's even more annoying than the phone issue above!
v31: Tap contact's icon, then the message icon.
v40: tap contact's icon, then the message icon, then choose between, "Message", "Audio message", or "E-Mail", and then YOU STILL HAVE TO PICK A PHONE NUMBER! Like I could even send a text message to a home phone! WTF!! And who gives a crap about an audio message when everyone has voicemail and/or an answering machine!
I'm personally finding this new contacts home screen really annoying! They have pretty much destroyed the usefulness of the contacts home screen since the number of steps required is now the same as simply opening the contacts app and going from there.
If there is some way to restore the older functionality I have not been able to find it. So be warned, if you will find the added nonsense irritating you should probably skip this update.