My 2c:
I migrated from the HR10 to the HR20 a while ago now.  It's been nearly-rock-solid for me (one bug that was fixed a few months back).  I'm a happy user.
I recently had the pleasure of getting a 2nd HDTV. 

  I hooked my HR10 up to it, so as to not miss out on any HD goodness.  A few days later, I flipped DVR's, and put the HR20 on my new 62" DLP, where the HR10 had been operating for a week or so.  Couple of points here:
1)  The PQ was 
CLEARLY inferior on the HR10.  And no, I'm not talking about a MPEG4 to MPEG2 comparison.  Same channel, same cabling, same program (I did it at halftime of the 2nd final 4 game).  Bad pixelation and whatnot on the HR10.  Much better on the HR20, and even better when I went to the MPEG4 feed.  I've seen descriptions of the HR10 as having a "soft" picture, but never something this blatant.
2)  The HR10 is slow.  Even with 6.3c (the latest software), it's slow.  Menus, guide, etc - ALL slow.  It was a drag going back to it after months on the HR20 as a primary.
I also missed the mini-window on guide / now playing list.  I know some hate it, but I think it's great.  I watch enough live TV (sports, etc) to make it totally worth it.
The ONLY thing I find myself missing from the Tivo - suggestions, of all things.  Why?  Well, I have 2 kids, and they like their shows.  I like my shows, my wife hers.  They rarely coincide.
Suggestions always kept the programs I don't want every one of (kids especially) churning, and updating.  Also turned me on to other things.  It did this without adding a new series record.  I'm now getting dangerously close to the 50 series limit on the HR20, and I'm hoping that gets at least doubled soon.
Anyhow - to answer the OP's question rhetorically, I'm going to retire my HR10 as soon as I can get an HR20 to replace it.  
