> So I assume you can take out the thumb drive and transfer it to
> the PC through the PC USB port

That would be desirable, as the thumb drive will be out in the field
with the product during logging. Periodically data will need to be
looked at back at the office, with the product still out in the field

One other possibility is to email the data through a GSM modem,
in which case the thumb drive will not be moved. Given that thumb
drive prices are through the floor it makes some sense to use one
rather than install on-board flash, although using on-board memory
in such a situation does rather mean that USB is no longer needed

But this is as much a learning exercise to make modern interfaces

> In that case, it is easier to do the following : PIC24 will act as the
> host to the USB thumb drive. Another PIC (PIC18F4550 or similar)
> will act as the USB device. You can use SPI between the two

Hmmm, OK, that's a thought
 
> If the speed requirement is not high between PC and
> your device, then you can save the 2nd PIC and use
> RS232 between the PIC24 and the PC. That is the case
> with the Microchip example.

I wouldn't want to get caught out trying to upload to a rep's laptop
for example that had no serial port. Although even this PC I thought
had no serial port until I spotted a COM1 header hidden away under
the modem card. A serial-USB adapter could be used if necessary
 
> OTG might be a possibility. But it is a recent addon
> to the stack and there is only one example which
> is the generic driver demo. So I think you need significant
> efforts to get it working for you.

Thanks for the advice. Once I get my head around what's actually
required to use the USB protocol the decisions should become easier
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