Per another thread I'm too lazy to search for, I inadvertently went 31,000 Km (19,000 mi.) on an oil change a year or so back. Added less than 1 litre/qt. in that distance.
Mine never has and I do check it a few times in between changes. I change at 3,000 regardless and use conventional oil. However the longer it stays in an engine it will breakdown and thus the level drops a tad. It also depends on driving styles. It also is normal for engines to use some when called for.
I just had a change yesterday after 8k miles (I use Synthetic Valvoline and was supposed to change by 7k, oops!), and they said my oil had dropped some (maybe a quart), but it was really dirty, so they ran a cleaner in the oil for about 10 min before the drain. It was most likely an unnecessary extra $10, but I figure it can't hurt it any!
Jason Damron, San Diego, CA, Supercharged 2004 Vibe base - Gone to the wind My Vibe pics on Cardomain2009 Chevrolet HHR SS!