I just thought I'd pass along my experiences, in case it can help others:
FWIW, I'm running a MacBook with OSX 10.5.6. I had a Keyspan USA-19 lying around from my old Palm Pilot. I tried to program my MiniPOV with this adapter and the Keyspan driver and it didn't work. I tried it with the PL2303 driver and that didn't work either. (I don't think the Keyspan has a PL2303 chipset, but I figured, what the hey?) Tried various delays, etc., still no go.
After reading an Amazon review where the reviewer said he was using a Trendnet TU-S9 for programing AVRs, I bought one for $13 at: http://www.amazon.com/TRENDnet-USB-to-Serial-Converter/dp/B0007T27H8
. It seems to be working great with the PL2303 driver. (I also picked up a banned for my daughter's birthday to bring my total to $25 so I could qualify for free shipping.)
Keyspan's website says the USA-19 (with no letters after the "19") is designed specifically for syncing PDAs and they don't recommend it for general USB-serial uses. Keyspan makes several other variations 19h
, etc. Others say they have been successful with Keyspan adapters, so it seems that some work and some don't. But, at least in my case, the plain USA-19 doesn't work.
I hope someone finds this helpful!