i avoid the first 5-10 min, depending on how the market is ticking on index futures. if i am trading fixed income, i just avoid the first couple of ticks.
you must explain in what markets you are talking about here. garbage in, usual et garbage out.
a lot of this talk is very dependant on your objectives.
most of the big money funds are putting their orders in on the open, and many of the big traders i know only trade the opening hour, then go home having made a big stack.
there is more to life than sitting in front of a screen.