So I did the 8.4 updates and held off on the 9.0.3 and found this topic on Debian forums:
http://forums.debian.net/viewtopic.php? ... es#p351587 which only has 1 message so far, essentially it says that there are now 2 instances of postgresql server running, 1 for each version. I only have a small database at the moment, 2 servers for 1 small database is sort of overkill.
After mulling it over I decided to set those updates to ignore (as opposed to installing and migrating my data), since I plan to dual-boot with CentOS 6 if or when it's released; and I don't know whether there will be support for v9 yet, and I don't want to end up with possible issues with not being able to have access to my data without jumping through unknown hoops.
I wanted to post this as a heads-up to anyone else to make sure you check what's being updated before you select the option to install them. (These are showing as a level 3 update in MintUpdate.)

