I don't think it's the USB controller inside the PC but the USB controller/driver in the axim or the controller which drives the SD/CF cards.
I use my axim on 2 different PC's:
own build with an Asus P4T-E
Dell GX110 equipped with an USB-2 controller
both high quality system that have no problems with USB (I use both PC's with a digicam, maxtor and WD external HD's)
my axim almost hangs when I transfer big files
and not only with USB, I get a max of 30KB/s with my WiFi card (100% signal, 11mbps) and the same behavior, unresponsive axim while transferring.
and the worst thing is.. when I get sick of it and abort my sandisk SD corrupts
