A properly designed HDMI device will not compress the audio. You should not hear any difference between a HDMI connection to your receiver and an optical (or coaxial) connection.
If your receiver will switch HDMI you have the advantage of not needing to switch the input on your TV and your receiver, switching inputs on the receiver will do both audio and video. If your receiver will also switch and convert s-video, composite and component inputs to HDMI your connections can be even simpler.
Again, if the HDMI is implemented properly there will not be any degradation in picture quality either.
HDMI 1.3 will allow for greater bandwidth which will allow for new higher bandwidth protocols but nothing in use in any receiver today will be affected, or needs the additional bandwidth that 1.3 allows.
I just asked a home theater expert what difference would there be using h.d.m.i. to your Amp Vs using optical audio connection. And was told the audio from h.d.m.i. would be compressed and sound quality would be slightly better using optical audio I was also told that h.d.m.i. 1.3 would correct this. Also would running h.d.m.i. thru amp then to t.v. degrade picture quality? I run all my vidio straight to t.v. and all audio to amp using optical cables and this set up really works great anyway beautiful day here in San Jose have a nice day all stewee