While killing the time waiting for an opportunity to test the PMD620 "in the field", I did some interesting experiments.
First, I checked all of the SD cards I could round up, in various sizes (256 MB, 512 MB, 1 GB, 2 GB, and 4 GB) from several manufacturer's (SanDisk, Lexar, and unknown). Some of these are quite old. All worked perfectly.
Next, I took the smallest of these SD cards, and recorded to the end to see what happens when a card gets full. The PMD620 properly closed the file and it (the file) worked fine.
I also looked at maximum file size. I recorded on the 4 GB card until the recorder stopped due to a full card. The result: a 3.78 GB file. I spot checked this file, including around the 2 GB mark, and it is a continuous file with no problems. It would be nice to check with an 8 or 16 GB SD, but, at least for the 4 GB, there is no effective file size limitation (this is just under 4 hours at 24/48).
I was also curious to see how the unit would respond to a power disruption. Using a pair of older batteries, I recorded til they died. The recorder gave a little note, and then cleanly shut down the file. I also tried pulling a battery, and pulling the AC adapter cord, while it was recording; in both cases, turning the unit back on gave a "restore" message and the files were fine. Lastly, when pulling the adapter with batteries inserted, the recorder shifted from socket to batteries with no troubles.
So, in short, some of the issues others have experienced with 2 GB maximum file sizes, seamless splits, or SD cards appear not to be problems with the PMD620. In addition, it handles power problems well...
Now if I could just find a good show to go to...