It seems that a lot of manufacturers think it is fine to just bundle a USB cable and a USB plug adapter but my understanding is that this gives much less power to charge the device than an actual proper plug build adapter. Through USB, my phone takes about 2-3hrs to charge but I don't own any USB micro plug adapters as they all end up breaking after a while due to their criminally bad design. I went through about 7 of them in 4yrs with my SGS.
USB Micro is truly the worst standard that has been imposed upon us all as with all the Nokia, Sony Ericsson etc individual chargers that came with phones before, I had 0 break through the lifetime of the related phone I was using. I have to say that Apple has got a winner there with the ThunderBolt and shame that nobody really has decided to use it since it was designed by and is owned by Intel not Apple.
With regards to you not being able to use ur phone whilst charging. I once bought a generic chinese USB micro wall adapter abroad and whilst when I tried to use my phone my digitiser would not work correctly (it did this with any phone) but it charged the phone within 1 hr instead of about 2 so I put up with it (until it broke lol).
