Ever since I've gotten 100% Synch on ACII, I've played with all of my HUD off except my Health bar, and even then that's just to know if I should heal when I fall. I find that when you don't use the minimap and un around the cities for a bit, you start to recognize places and monuments. And as a quote from my friend; "I love this game. If you're ever confused, just climb a building." He's right. If you have no clue where you are, climb a building, look for viewpoints you recognize, look for exits to the city (Fast travel locations), etc etc. It's actually really fun NOT to play with a mini-map.
Yeah, until you start doing side missions. Then it becomes a pain. Ezio seems to know where to go all the time without the need for directions. Every assassination target i had to constantly bring up the map to find the green area, same for courier and beat up missions.