I've had the 3900 for a few months now, and it is a very nice receiver.
I have 3 722's hooked via HDMI to an older Samsung DLP (1st gen HDMI), and have no problems at all with resolution switching on me.
The 3900 does not have the auto volume leveler.
It has a network port which plays internet radio, streaming music from other network computers & allows web access to it's built in webserver for control. It also has a serial port that you can use for control (I use Homeseer to connect to that port). There's also receiver manager software that can be found to change settings via network, and save them to a file on a PC.
The YPAO works really well - auto setup of speakers from single or multiple spots.
A couple of features I miss from older Yamahas:
1) Choosing an audio only source (tuner, net radio) forces the video selection as well - used to keep the last selected video source displaying
2) no A/B speaker switch - you have to navigate a menu to assign the speakers to zone 2 or 3, then use the zone 2 or 3 power to turn them on & off.
3) you can use one of the extra amps to drive the front presence speakers or the back surrounds - not both at the same time. This changes the 8-speaker sound mode I was used to into a 7 speaker mode.
AVS has a forum for 3900/1900:
"Official" RX-V1900/RX-V3900 Thread - AVS Forum
Some reviews:
Playback Magazine | Issue 19
Sound & Vision Magazine - Yamaha RX-V3900 A/V receiver