I have a 105 groupset on my 2007 trek, not exactly sure what model number it is. I find that the shifting is smooth enough, but I really get annoyed at the long shifter throw length when moving to a larger cog/chainwheel.
I am considering upgrading to ultegra 6700 shifters, 10 speed cassette, and 6700 RD. I would like a different size cassette, and having 10 speeds but its going to be hard to justify the cost of upgrading to ultegra shifters unless I will see a difference in throw length.
If the 6700 stuff is not a big difference, I'd be open to SRAM or campy stuff if they are.