On both of my test systems, plus several others on which I have installed Windows 7 RTM (including Lenovo T60p and X61 laptops), driver availability for recent-model systems (3 years old or younger) was surprisingly good with just the installation media--and even better upon first connection to Windows Update. On all four systems mentioned above, the only device that could not obtain a driver in this manner was a wireless WAN card in one of the laptops. However, the functioning of the drivers was still a little dicey in some cases. With the Lenovo X61, for example, the 64-bit Win7 video driver for the laptop's Intel 965 chipset adapter technically worked, but only with a lot of tinkering--particularly with an external monitor attached to the laptop's VGA connector. In this case, getting the external monitor to the maximum supported resolution required me to periodically re-adjust the monitor refresh rate.
I expect Windows 7's driver support and performance to improve significantly before the operating system's official mid-October launch. However, don't expect legacy support for older devices to magically appear. If a vendor never created a driver that worked well with Vista, don't expect one to show up for Windows 7.