I've not tried human opponents yet, for this very reason! I think you can easily get into some bad habits versus the AI, certainly the 'Vegas mentality' displayed in the first post affects me playing against the computer.
I only recently bought CMBB, having had CMBO for a little while, and heartily enjoying it. After downloading what felt like a million megs of patches I tried a quick mission game (God bless whoever designed this format. It's heaven!).
I played Axis attacking on a reasonably flat map with moderate tree cover (which turned out to be the village type with diagonal road crossing so familiar in CMBO).
Things went surprisingly well. For a start, the AI opened up with a medium tank at extreme range. Educated in CMBO, I expected instant death for the Medium tank he was shooing at. In fact all his shots ricocheted, and my tank plugged him effortlessly in one shot. So far so good.
The trend continued, and I was able to steadily advance right on top of him. Here's when I got sloppy. He had two guns (I never found out what they actually were!) right at the back of the map, next to each other in a small wood. They were actually quite ineffectively placed, only able to cover the bottom quarter of the map, and limited in LOS by the village buildings.
Well, idiot here marches 3 medium tanks in. They got knocked out one at a time. Should have learnt my lesson after the first. So I sent two half tracks in left and right, to try and supress them. Both got knocked out. Eventually I brought my 50mm mortar man into a house nearby and just Arty'd them..but you get the point.
I broke all my own simple rules about mutual support and coordination...again. I won the scenario, but couldn't help but think a human opponent would have harried me all the way, and generally made life difficult.
Shame the AI still tends to open up far too early on these quick maps. It encourages my laziness.