This isn't really a new or a bug, since the same limitation existed in the
RH 6.1 installer too. With previous versions, the (text-mode) installer
gave a running total size in MB for all selected packages when doing the
individual package selection. This is extremely useful when installing on
a system where space is constrained and you can't install everything.
The new installer, both the X-based GUI and the text-mode interface, no
longer give this running total, making package selection much more
difficult and error prone. (You find out if you're over before it begins
the install, but then you have to go back, possibly more than once, and
fine-tune your selection until it fits.)
This issue has been added to a list of feature requests for later releases.
This has been completed, and will show up in the next release.