The Yamaha iPhone/iPod touch control application
is nice for those with one of the supported models, but it can pretty easily be made to work with older models that only support RS-232 control (e.g. RX-V1700/2700/1800/3800/1900). The Yamaha App needs to know the IP address of the receiver on your network, but instead you can give it the address of a PC that's running a program to translate network commands into RS-232 commands. Any old cast-off PC is good enough, and it can be located in another room connected by a long cable, so it's not in the way and can be left running all the time.
I just got an iPod touch and did a few tests to confirm that the Yamaha App can easily be fooled into thinking it's talking to a real receiver. I hope to have it controlling my RX-V1800 soon. It should be a good solution for those with equipment that's out of sight, or for whatever reason can't read the front panel from where they sit (e.g. when listening in another zone). The Yamaha App is fairly limited in what it can do though, and a custom control App could do a lot more. Problem is you need a Mac to develop custom applications and I don't have one, although I might break down and get a Mac Mini before long.