Quick way to check if your blade is square to the table: Cut about 1/4" into the edge of a 2x4, back out of the cut, slide the 2x4 around to the back of the blade, the blade should slide right into the slot you just cut. if it doesn't adjust the table until it does.
I keep one next to the saw maked with which blade made the cut. Makes it quick to readjust the table back to 90*.