SD had a 1GB limit that somehow got extended to 2GB. Most older devices will NOT accept cards larger than 1GB. The upgrade from 2GB to 4GB needed a hardware change. If Edirol mentioned a 2GB maximum in the R09, assume that they mean it until they say otherwise. It's not like CF where "2GB maximum" (former spec for the PMD660) meant "they didn't have a 4GB card in the shop and haven't tested it yet". 4GB SD cards are incompatible with older equipment and my guess is that if an upgrade is possible, it will require sending the unit to the shop for a hardware mod. Nonetheless, 4GB isn't so terrible-- even at 24/48 it's over 5 hours of recording, and in mp3 it's near-unlimited.
What I really want to know and nobody has said is how long you can record without a battery swap (assume two 2500 mAH AA NiMH cells). With the PMD660, I can record for 6+ hours (maybe almost 8 hours if I push it) on four AA's, and in fact I do that all the time. I'd like it they made some kind of accessory battery pack for these things like some digicams have, that held 8 AA's or whatever, allowing 12+ hours nonstop recording (in mp3). Yes, I really do want to do that, at all-day or all-night events. The PMD660 is not the greatest machine I can imagine, but its battery runtime is pretty good, at least double the R-1's from what I understand.
The R-1 manual also said that the recording could get screwed up if the recorder wasn't shut off properly, i.e. if you just let it run til the batteries crap out, the file can get clobbered. I hope they fixed that with the R09. This is one of the reasons I bought the PMD660 instead of the R-1. I've let the batteries in the PMD660 crap out many times and nothing bad has happened, the file just ends when the power ran out.