Within a few weeks, the linux community added drivers to Linus' stack. In november, a few people did a rewrite, which gave an improved driver, interface and performance. You can have 127 devices, including hubs. The bus is self-describing, you have device descriptors.
Configuration allow for varying functionality and levels of power use.
As far as device support is concerned, you have both OHCI and UHCI host controllers and the one you get depends on the vendor. It's however a good idea to use libusb because that binary control interface may change in the future. Other issues are bandwidth allocation and management, power management, and USB 2.0.