After watching many Let's Plays and noticing how much thought I put into organization of my own hotbar, I've come to the realization of just how important hotbar organization is in Minecraft. And yet, I've never seen it discussed before.
Personally, I go with this arrangement:
1. Bow or, if possible, item enchanted with good knockback
5. Solid, placeable blcok (usually cobblestone)
7. Gravity-affected block (sand or gravel)
5. Map (I get lost very easily)
I wish now that I'd put the sword in the first slot so that it would always be the first thing I'm holding when I start up. But it's too late now; I'd constantly be hitting 9 and fending off creepers with a shovel.