I'm recently back - USB on the Amiga - What can I do with it?

[Thomas]

Can I access 2-4GB flash drives.

Yes.

(If yes, could I boot OS 3.9 off them?)

Only if your USB card has a flash ROM which holds the drivers or if you have another expansion with flash ROM.

The upcoming Deneb has a ROM AFAIK, the Highway for example has none.

USB CDRW

Yes.

Hard Drive support?

Yes.

Can I use any USB RJ45 Network Dongles?

Not every, but there are drivers for some (check the software's documentation).

Keyboard and mouse?

Yes.

Any others that I missed that are supported?

These are supported (no joke): http://www.lifeaftercoffee.com/2006/10/24/usb-missile-launcher-hands-on-review/

And of course each device which uses the USB connection only as a power supply, for example: http://www.getdigital.de/products/usb_aquarium_klein/lng/2

But be sure to use a self-powered hub for those.

what options are left for Scan Doublers so that I can connect my A4000 to my LCD monitors through my KVM instead of having to add space for my old Multiscan 15" monitor.

Replace your LCD monitor by an LCD TV with both VGA and Scart (RGB) input.

Or, if you don't run games or other programs which insist on a native Amiga screenmode, buy a graphics card.

Bye,
Thomas