Although the teflon coating does slow down the gunky build up on the throttle body, it does not prevent it. The teflon coating does need to be treated with care, but the throttle body still gets dirty and still needs cleaning from time to time. I clean mine fairly often (at least every 10,000 miles) and I can definitely notice an improvement every time.
This topic has been covered many times and you should be able to find detailed instructions with a search.
