I've been making burger's a long time...one thing I've recently altered in my approach? I was raised to smack patties together aggressively so that they would stay together on the grill. But I think one of the keys to a really great burger is to put them together loosely, preserving as much of the individual 'ground beef threads' as possible. In other words, pack the patty as loosely as you possibly can and yet keep the patty together when cooking on the grill. The difference in the final product is pretty dramatic.
As far as tasting the mix, no answer there, although in my experience, its tough to dramatically impact the final taste of the patties based on 'additions'. Hamburgers are pretty forgiving. I think the late additions (like cheese, toppings, sauces) at the end of preparation have a lot more to do with flavor than anything you add to the meat itself. That's another thing I've shifted on...I'll still add some things to the meat mixture, but I don't go overboard on that front.