ADVANCED: This article describes how to update your USB drivers on certain systems to allow higher current charging if only one device is plugged into that group of ports. I will be updating this as i go along but this works on my PC's with ASUS motherboards ( ASUS and HP ) and so far it is working on my Lenovo Thinkpad T400. This may provide the perfect marriage with the Y USB power splitter cables. If anyone has pinout for one of these cables, please contact me. Amazon and other vendors sell such cables but I'm curious as to the construction. Just marrying the +/- 5V does not appear to be correct. DISCLAIMER: warning, there is a chance that this could burn out your USB port or device, though most good boards should protect themselves. Not responsible for damages, no warranty expressed or implied, risk of fire, etc.
This seems to work on boards with Intel ICH9 and 10 chipsets. ASUS has published a driver update that seems to work on some boards with Intel USB root hubs. I have not tested it yet with the iPad battery below 80% where it would draw more power but it worked in the top end. I was able to have the device awake playing Pandora and it shows charging AND the battery level increased. When I attempted to plug it into a port where there was another USB device on the same 'hub' it disabled the internal hub and both devices lost power. Was able to reset it and separated out all my devices.
Not very fast, but screen was on and charging and 'active'
MouseOver or firm tap ( iPad ) for enlarge
Checklist
Have good cable and understand iPad and other power requirements, see this article.
Please read up on USB and understand what you are doing.
Cross fingers
Procedure
Note: I have not tested rollback procedure via uninstall drivers. If you have a lot of USB devices, this may have side effects. Backup your system first or take system image. If it is too late and you didn't read carefully, try to redistribute to other ports or a powered USB hub. Also, I do not know what would happen ( good or bad ) if your USB ports are not compatible with the drivers. Probably will just ignore them.
1) Read warning at top again, then get drivers here. It says XP Vista Windows 7. It works on my Thinkpad running Windows 7 64-bit professional.
2) Reboot ( surprised? )
3) While you have multiple USB ports on your computer, they are often shared internally by 2-4 other ports. Because the iPad and iPhones want more than 500ma, you need to make sure no other devices are on the same 'hub' so that you can take all the power you can get. The good hubs will protect themselves and disable if a device draws more than it can provide.
4) If you have read up on the USB and want to risk damaging the port, plug in your device.
5) Check the port where it lives
Conclusion
Working so far. I need to track down the schematic / pinout for the USB Y splitter power combiner cables to see if this helps more. Such cables may reduce the load on the ports also. Will update when I test the charge when the iPad is more depleted. It may require more power than it can provide. Again, there is risk of damage to system or devices. Whenever working with batteries and power there is always risk of fire or burns.
Update
As of Aug 1, 2010 it is still working on my Thinkpad. I now get errors if I plug to many components into a pair of USB ports on the same power bus, but it seemed to reset the port ok. I am just not using the other port. Also, with a good cable ( built one with 20 AWG power pair ) it charges my iPhone 3GS really fast now off USB.