Capt. Tom: I'm not sure what his reasons are, but I change mine bothe in fall and spring. It's cheap and easy piece of mind. I actually change mine about 5-10 times a season, but it's because I know a bit of water finds it's way into the lower unit. Some lower units have small leaks around the propshaft, or even fill plug, that could theoreticly drip all winter.. Underneath my outboard there is a nice black spot of carbon/fuel/winterizing oil.. this is pretty common, it's hard to tell whether or not any of that is gear lube. The gear lube can, and should, be checked if you aren't going to change it - by sticking a zip-tie into the vent hole. But, for me, it's just as easy to change it.
SeaJay - Never run anything other than 87 octane in any marine engine (yes, other than deisel). The reason for it is that to boost octane, additives are put into the fuel. These additives are mostly alcohol; this tends to absorb condensation, increase wear of fuel lines, engine components, clog carbs and is just generally bad - the same reasons are why you never use dry gas in a marine engine.
MeanBean: I disagree on changing the plugs - you may have to clean them... if they are a few seasons old or corroded, change them. If they are stainless & $8.00 a pop - that's a waste of money to replace every season, some of those are good for a lifetime.