I mentioned this wish in another thread already, but the single most important thing I miss in the application manager is a button for New Packages.
It should be just the the current one for new upgrades, but it should instead show new packages that have become available since the previous time you hit the 'refresh' option.

For those using Debian on the desktop, there's a command line tool 'wajig' which is essentially a wrap-all command covering apt-get, apt-cache, dpkg etc., and it has two important commands: 'new-upgrades' and 'new'. The command line sequence is then typically:
wajig update
wajig new-upgrades
wajig new
(and then you decide whether to upgrade, or to wajig install (or apt-get install) any of the new stuff)

The equivalent for application manager would be:
refresh
check for upgrades
(missing) check for new packages

As it is now, if you want to see if there's anything newly available since the last time you updated you'll have to wade through that (bigger and bigger) list of available applications, and try to spot the new package(s). Not nice.