The Pros: Mouse pointer integration is built-in, so you don't have to deal with reinstalling Guest Additions every time you do a kernel update.
The Cons: Since Maverick started using a new X-Server (1.9), Guest Additions no longer do their acceleration and resolution magic. This includes manually adding resolutions to the xorg.conf, so until something changes, it's 800x600 all the way...
UPDATE (9/30/2010): Looks like the open source edition of VirtualBox has us covered now. Just open up a terminal and type (all one line):
sudo apt-get update ; sudo apt-get install build-essential linux-headers-$(uname -r) ; sudo apt-get install virtualbox-ose-guest-x11
Thanks for the tip, Anonymous!
I'm putting this here for my own reference, but if you want to automatically mount your host's shared directory in your Linux guest OS, you can edit /etc/fstab thusly:
[host's name of directory] [mount point] vboxsf defaults 0 0
which, for me, translates to:
vbox_share /media/vbox vboxsf defaults 0 0
No more tedious mounting and no mucking around with startup scripts running as root...
Something else I've encountered, not specific to Maverick, but I figured I'd share it here anyway:
I decided to give BTRFS a shot, so I formatted my partitions with it (it still won't support booting, so I had to make a small boot partition with ext4, but / and /home are BTRFS). Unfortunately, there is a hellacious bug somewhere that causes apt-get update/upgrade to be godawful slow (like, 4 hrs. for a big-but-still-reasonable upgrade) with this FS. However, I came across this blog post that suggests using a patched copy of dpkg, which is available from this ppa, which specializes in BTRFS-optimized packages. To add the PPA, add it to your sources in Synaptic or open a terminal and type:
sudo apt-add-repository ppa:brian-rogers/btrfs
Then just update/upgrade as usual. The package comes with a pretty scary warning about how it can hose your system, so you should take frequent snapshots (that's why you're using BTRFS anyway, right? Right??). Unfortunately, this didn't really fix my problem, so it's back to ext4 for me. :(
Once perk of reinstalling using the latest Beta release package is that I got to check out the new installer. It looks really nice and they've done some really smart things with concurrency whereby it starts installing your system before it asks you all of the time-consuming personalization questions. All in all, installation was easy and fast, fast, fast!
Everything else appears unchanged since Lucid.
I'll update this post as I find anything else out. If anyone has anything to add, feel free to leave a comment.