RE: cannot act as a RPC client:
I believe it will still be able to act as a RPC server.
So you can run the GUI with the -server switch, but you'll have to talk to it using (for example)
bitcoind getinfo
... as opposed to today, where you can run "bitcoin -server" to get the GUI and then run "bitcoin getinfo" to talk to the running GUI process.
RE: why switch: because no wxwidgets programmers stepped up and made it better. And from what I can see, QT is more popular and supported (so there are more programmers able and willing to help improve).
RE: screen shots: See the bitcoin-qt thread in the Alternative Clients sub-forum here.