This ‘app note’ was posted in the forum by rsdio. Great advice for designing USB devices for proper current and maximum power:
There are some common misconceptions about USB Device design with regard to the amount of current available and the MaxPower field of the USB Descriptors. Many DIY developers simply enter the maximum 500 mA value without consideration for the actual rules and ramifications. Some may think they’re playing conservative by entering 100 mA instead, without realizing that they may still be in violation. This topic is intended to illustrate the situation as quickly as possible and open up a discussion if necessary.
Image: Magnus Manske (CC BY-SA)