I just got the 825.  I wanted gigabit capability, plus my old Linksys didn't support WPA.  I did a lot of research before-hand, so I knew what i was getting into.  Here's a quick summary of how things are going mostly trouble-free.  I am overwhelmed by all the possible settings, but that seems to be standard for these types of routers:
- Installation went quick, although the quick-setup didn't cover all the main issues.  I had to change the internal address range from 1-100 to 100-255 due to previously assigned addresses that I wanted to keep.
- all the software I have (games, BT, communication) had no issues with the new router.  I didn't use any special rules, just out-of-box setup
- I disabled the 5GHz range since I don't have any "n" wireless units.  I also forced it to use "g" at the highest transmit rate
- The Wii had no issues connecting, faster than the old router
- Problem #1 is that my ubuntu laptop can no longer see the Windows network neighborhood.  I can connect via IP, but can't browse the system. This must be a security setting somewhere.
- Problem #2 is that the wireless connections seem to drop when they are idle.  The Wii is fine on Mario Karts, and there is no drop.  But a laptop sitting unused or just reading a long web page may sometimes drop.  Streaming video (hulu) isn't affected, though.  Not sure if this is related to the drops that everyone else is talking about.  
I haven't used any of the advanced features like QoS, WISH, etc.  I'll start playing with them one at a time.