Well it is possible to charge and have the Galaxy Tab in host mode at the same time. It took us a good while to figure it out but it has been done.
We have built a little cable with 2 usb connectors on the end - one for charging, one for a USB host device such as a usb-memory stick, keyboard, serial port etc. Note, you can also connect a hub.
The circuitry to do this little trick is quite complicated and requires a state-sequential machine (cpu) to cycle the tablet whenever charge power is applied. The unfortunate negative of this is that whenever charge power is applied the tablet will disconnect all host devices, enable charging and then reconnect the attached devices. If charge power is unplugged later on the host mode is not affected. Charge rate varies with battery level. The highest rate (about 1.7 amps will be achieved when the tablet is near or below 10% battery charge. As the battery becomes more fully charged the tablet automatically reduces power draw. Once fully charged the tablet will draw about 700mA with screen full on (full brightness) keeping the battery at full charge.
Roman Wynnyckyj
Lava Computer MFG. Inc.
LAVA: The Source for Ports - Serial Port Experts