I forced the upgrade yesterday at the direction of D* tech support. She told me it would speed up the guide (which, of course, it doesn't)
Haven't really noticed any differences.
On a side note, in a span of 2 weeks I now have had two H20-100s and one H20-600 (refurb)
The first 100 died during the second day of use.
the 600 was fine, but after experiencing the quicker guide of the 100, this really bummed me out, so I asked for another replacement.
The second 100 had audio dropouts every 10 seconds when using the optical digital audio out. And picture freezes, every couple minutes.
Ughh. After all that, I've hooked the 600 back up and will probably just deal with the slower guide.
(Also, SD on the 600 looks a bit better to me than SD on the 100)