Its been hit and miss for me. My car stereo and cigarette adapter do not work. One USB port on my computer works, the hub does not... etc etc.
Does your car stereo and cigarette adapter charge your iPhone 3G or 3GS?
Many (most?) car stereo iPod cables and many (most?) iPod cigarette lighter chargers charge via the 12v Firewire pin found on older iPod models.
Background: When Apple first released the iPod with a dock connector, they provided TWO power pins for charging within the 30-pin dock connector. One pin was designed to be used with a Firewire port (which is 12v) and the other pin was designed to be used with a USB port (which is 5v). For several years, all iPods made continued that same tradition of supporting both charging pins. However, in 2008, with the release of the iPhone 3G, Apple DROPPED support for the 12v Firewire charging pin. They also dropped that pin on subsequent iPod models. The only iPod model that continues to support the 12v Firewire charging pin is the iPod Classic.
Anyway, since a vehicle's standard electrical system is 12v, the majority of car stereo manufacturers and iPod cigarette lighter adapters simply designed their products to use the 12v charging pin. Oops.... Apple dropped support for that pin in MOST iPhone/iPod/iPad products since that time and now those 12v chargers won't charge the newer devices.
So, the most likely reason your car stereo or cigarette lighter adapter won't charge you iPad is because they use 12v, not the 5v USB that the iPad requires.
Slowly, manufacturers are figuring out they need to change their products to support 5v USB charging on that different pin. But, in the meantime, you can use one of these to correct the problem:
http://www.scosche.com/products/sfID1/210/sfID2/318/productID/1667
That device (and other like it) convert the 12v pin power to 5v and send it to the appropriate pin.
And, for those interested, Scosche also offers USB cigarette adapters that support the iPad:
See that 2.1amp port, that one is for the iPad!
http://www.scosche.com/products/sfID1/210/sfID2/318/productID/1921
Mark