How simple/easy is it to adjust the carb. idle on my 05 FB? It runs great but when it is all the way warmed up, I would like to have it idle a bit slower.

 

It's easy. There is an idle screw at the top right
Side of your carb near the throttle cables, turn it
Counter clockwise for slower idle.

 

This image is when you're looking over the TOP RIGHT side of your carb and looking inwards. Notice it's the screw with a spring underneith. I just had to help my buddy out the other day and did this on his '94 Dyna.
Oh, and don't go wild turning the idle TOO low - you don't want to reduce proper oil circulation pressure. I think they recommend 900RPMs for the Twin Cam?

 

There are two carb adjustments you need to make. (1) Idle Fuel Mixture and (2) Idle. Twin cam engines must idle between 900-1,100 RPM otherwise your top end will be starved for oil. Don't try and get the potato-potato sound!!!

Invest in a Harley Service Manual. It will be the best money you'll spend.