Well, I can tell you this...

I have the good old vintage stuff (clips and toestraps). Ive never had the clipless stuff. Its funny, Im almost 23 yet I still prefer the old stuff. ANYWAY...

I can stand for a few minutes with my clips. I dont see the differance with clipless. To me its all about the balance. The only tip I have is of course practice, but I found that, for example like me, when I have my left foot front, I keep my right inner thigh touching the right side of my seat and hover over your bars like there is no tomorrow. Keep it steady and dont budge and youll be fine. If you want it more in depth...

http://www.63xc.com/gregg/101_12.htm

Good luck, and a few cold ones dont hurt