I agree with Docpepz that KL Sentral is not exactly located in downtown Kuala Lumpur. However, there are LRT (Metro, subway, MRT, tube whatever you call it!) services that run from KL Sentral to KLCC which will take you there within minutes. I agree that Bukit Bintang is a bit far off to reach, but then, there will be LRT services in the future, I think either in 2003 or 2004 linking KL Sentral to Bukit Bintang area. Actually, if you really want to go to downtown, you could well take the LRT to Masjid Jamek station or to the KLCC station. Bukit Bintang is merely a shopping paradise, not really much of a business district.
By the way, if you want to blame on the bad roads in Kuala Lumpur, blame it on someone who planned it years ago who did not planned it with straight roads, but instead with roads that are curving here and there. I like the way that most American cities are planned where it's easy to navigate around!
The KLIA Express people are planning to come up with more tariffs available to the public. They are seeing how things are going first in the first month of operations.