i have put twenty hours on the boat this summer so far, and it looks like my drive lube has gone down about 1 1/2 to 2 inches from the fill line. There doesn't appear to be any water in the resevoir. Is this cause for concern, is some lube usage normal, or not, i am going to top it back off and watch it a bit closer to see how it does.

Look all around the exterior of the drive for any oily spots. You also might pull the prop off and make sure it'd not leaking past the seal on the shaft.
Could there have been air pockets from when you changed your drive oil before the season started, that simply filled up?
I agree, watch it close. Make sure you aren't getting any water in the dirve. It doesn't lubricate very well.

yeah, i just bought the boat, and he had it done at the end of last season, so i will add some and top it off and see what happens

If it continues to go down, I would do a leak check around the drive and then maybe pull the drive off the transom assembly. If the front pinion seal is leaking it will show up in the bellows.
When I finish a drive, I pressure test it for 12-24hrs at 10psi. I made a little adapter from a oil fitting from a small block Chevy. It has a gauge and shroder valve to fill it like a bike tire. If it leaks down, I take a closer look.
I would suspect that you will find that it wont use anymore and you are good to go for the season.

Good luck

Dick

it took about 4-5 oz. to top off, what brand of fluid are you guys using, i have a bravo one

when you fill 'em...fill em up into the reservoir and voila! no air pockets! using the pump up can, just watch the bottle, and shut off the fill valve about 1 inch below the full line (about where the strap is). It's 2 person deal but even the wife or a kid can tell you when you're there. By time the pressure in the can is nil...it will be right at the fill line, and you won't touch it again. Yes, "green death" but with frquent changes.