Thank you for all the feedback between the R-09HR and the 620, but I've recently been hearing about the LS-10 and have been wondering how it stacks up. It certainly looks impressive, and the 2gig internal memory doesn't hurt either! I wonder if one could use the internal but still have a card in the slot?
You can certainly use the internal memory when a card is inserted - this can be selected through the menus, or you can set the user-definable
Fn button to switch between the two. The LS-10 will
not auto-switch between the internal memory and the card, though.
My own policy is to use internal flash only when absolutely necessary, since flash has a finite number of read/write cycles. I haven't seen any information on the lifetime of the built-in flash, though. That being said, 2 GB isn't a whole lot if you're recording in 24-bit mode, even at 44.1 kHz. I've used SanDisk 4 GB and "Polaroid" (really PNY) 8 GB cards without any problems.
Be sure to load firmware version 1.10 if your LS-10 isn't preloaded with it. The 1.10 firmware seamlessly auto-splits files when they reach 2 GB.
As long as you take into account the baked-in bass rolloff on the internal mics and mic-in (but not line-in), you can get excellent results with the LS-10. Be sure to use the low sensitivity position for music recording - otherwise you'll get even more rolloff. EQ can take good care of rolled-off bass if necessary - but if you're using bass-heavy external mics, EQ isn't really necessary.
The internal mics are on the bright side, but that's what post-production is for.

For my classical recordings, I haven't considered them to be excessively bright.
Line-in needs a hot signal - unity gain is at recording level 10.
Battery life is outstanding. I know I've been able to get at least 8 hours on a pair of alkaline AAs before chickening out and replacing them. Olympus claims 12 hours.