Hey Steve,
Don't take it hard on yourself.
Alot of what needs to be said has already been said and this is where field experience really counts.
Reading over what you said, I can say right off the bat, its tough to be using flash at a car show because the cars will reflect alot of light and may bias your exposure leading to severely underexposed or dark backgrounds and an awkwardly lit car. This is a common problems with flash I find. That's not mentioning the reflections on the body you might pick out.
You also mentioned colour balance. Typical lightning in tradeshows, indoor events tend to be rather challenging to correct for. If you use a 'naked' flash, you introduce alot of light of another colour temperature so now your camera has to pick and choose. If you set your WB preset to flash, your background/ambient light will not be corrected. If you choose the correct WB for your ambient light, your foreground lit by the flash will be off in colour.
Steps you might wanna try when walking into any event if you haven't already is to try ambient (cuz you got DA* 2.8 zooms!) as well as your flash, but use a diffuser or bounce card. Maybe a gel that is close to your ambient colour if you are willing to go as far as that to reduce the disparity between your flash colour temp. and your ambient temp.
Don't be alarmed. It happens to everyone regardless of brand especially with flash exposure. It took me about a year of on and off trial and error to really begin to understand the fundamentals of flash exposure using a manual flash. Being able to piece together foreground, ambient and what settings to adjust etc.
Hope it helps and don't think just cuz your buddy has a Nikon, you gotta switch. The rules of the game are the same regardless of brand.
If you still don't believe me, I'm like the only Pentaxian at school shooting alongside Canon's, Nikon's, Olympus dSLR shooters for three years. I've rarely ever been tempted to switch.
Last edited by FotoPete; 04-26-2009 at 06:23 PM.