I got my unit last week, and set it up to run in Native mode since I wanted the best picture possible. My TV is a Pioneer Elite Plasma, which purportedly has great video scaling. I'm running 0xD8, btw. I've found that doing the 30 sec slip and 6 sec replay thing sometimes made the HR20 forget which resolution it was outputting, forcing my TV to relock. Even worse, the HR20 would sometimes drop audio when resuming playing (which would come back if I paused again and then hit Play).
With Native on, it detects it automatically, but the trade-off is that currently there is a delay as it figures out which resolution to switch to.
So, here's the tip: Switch to Native Off, 1080i mode. Now the HR20 will stay at 1080i even when fast forwarding or replaying. The audio hasn't dropped out on me yet in this mode. It does mean I'm scaling video up in the HR20 instead of the TV (which is actually now internally scaling down to 768p), and I can tell the difference on SD material (it is slight), but HD material looks the same or even better. Overall, it's worth the trade-off, IMO.