I make a habit of checking my oil every few days. I don't usually lose any unless I make repeated high speed runs, but I still like to be on top of it. You're probably losing a little to blowby; the amount you lose is dependent to some extent on how hard you drive the car as well. If you drive harder, you'll create more high pressure situations in the crankcase, and you'll get more blowby. You also might have a leaky rear main seal and/or oil pan gasket. After my 60k I found that I was still losing a little oil, although the drip I had from my front main seal had stopped. I was a little confused until I realized that it was probably coming from the rear main seal and pan gasket (I later found I was correct and had both seals replaced with my clutch). These two seals can leak, but you may never see it as it can get caught up on the subframe, it can adhere to the pan due to dirt and road grime and may appear as gunk rather than leaking oil, and your rear main can get all caught up in the transmission bellhousing.
