I just purchased the 717 on Monday. HOLY COW!, best AVR I've ever had or listened to. Easy setup, audessy did its thing and it never sounded better. I have a 7.1 system, atlantic technology speakers. Very expensive speakers, actually fits right into the 3.1 or 2.1 speaker to receiver cost ratio. The only complaint I've heard about the 717 is users wish they had the upgraded version of audessy. The thing is like I mentioned, it did the job for me, I don't have to mess with the EQ or settings, it automatically did it for me.
The 616 did have some firmware issues, I have yet to update my firmware, but haven't read anything about issues with firmware with the 717.
With receivers, you really just have to decide what is best for your room. My theater room is 20x12, so I did my home work and set a price range. Funny thing, last week the price of the 717 was $589, when I purchased it, I got it for $632, it's now up to $700 and up, maybe the 818 isn't what buyers thought it was.
The only issue I've noticed with the 717 is it does get a little warm, but almost all AVRs do.
The video processing is awesome, the days of analog and cables running through the walls and ceiling are over, Easy hook up with HDMI and your off to the races.
Bottom line, set a price and do your research and your needs for your room and then make a list and start researching them. You can't go wrong with the 717. Me personally, the difference between the 717 and the 818 wasnt worth paying $300 more and I'd be willing to bet I wouldnt have noticed much difference between the two.