The update, described by the Windows Phone Blog does more than just support Mango. If you connect your phone with Zune and there are multiple updates available, you only have to interact with the software one time to get all of the updates loaded. Previously, you had to apply each update separately. While Microsoft hasn't released multiple updates at once, more than one carrier held back the updates and users got multiple updates simultaneously.
For me, the real fix is to get carriers to quit doing that, but at least if they do, the update process is less of a hassle for the end user.
The backup process is also faster. Media is now separated from other phone content, so a backup doesn't involve transferring 10 GB of music, all of which is in your Zune library anyway. If your computer is low on hard drive space and you cannot perform a backup, even excluding the media, you will now have the option to skip the backup and proceed with the upgrade if desired.
I think it would be a better idea to temporarily move a few gigabytes of data to a USB key and have a backup made just in case, rather than perform the upgrade sans backup, but some prefer the excitement of plowing forward with a major upgrade with no safety net.
Version 4.8 is available in 22 languages in nearly 40 countries or regions, so if you haven't been able to get it before, see if your area is now supported.
Additionally, there are some small changes with how you buy content. For example, 48-hour movie rentals are available now and parental controls support mature (M) content.
Microsoft is definitely ready to go with Mango. Now we need to wait on the carriers. Is Mango showing up as an update for you yet? Yeah ... me neither.