Don't know for sure about the max size, but the docs say 8Gb. I suspect that will be higher with patches and hacks, etc..

Stock, the N810 has 3 "drives": The 250Mb system (partitioned in Linux oddness), the internal 2Gb flash (soldered in, not removable), and the removable mini-SD. The internal shows up as mmc2 and the external as mmc1. The system can use up to 128Mb of the internal flash for swap-file space, but that's about is as far as system files.

Now, this is stock, but you do have a choice. It appears that people are running boot-loaders and putting alternative OSs in the internal or external flash. It's an open system, how much do you want to play?

David...