this thread reminds me of a funny story...
when i bought my 01 gsxr 1000 (got it used at a repo auction in Jersey) I rode it a few times and was seriously dissappointed with the power it seemed to be putting out.
I had read that suzuki limits the power in the lower gears so i figured that might be the cause of the problem. getting the front wheel in the air was not nearly as easy as with my R1.
So, I was pretty quick to install a TRE, and a power commander as it had an aftermarket pipe, but neither of those two things helped either.
Anyway, i go up to my local shop to pick up an oil filter and spark plugs etc so I can do a tune-up on it (I do this whenever I buy a used bike) and I figure I will have them take it for a spin and see if it feels down on power.
One of the guys that works there has the exact same bike, takes it out and comes back and says that it feels a LITTLE bit low on power but nothing to worry about.
I'm not satisfied, so I ask them to put it on the dyno. after the run, the guy tells me that it is putting out 115. thinking i misheard him, i said 150? that isn't too bad. "no" he says, "1-1-5". I'm royally ticked at that point and I figure i've bought a piece of junk.
So they start working on it and luckily the first thing they did was start draining the oil. turns out the moron who owned it before had seriously overfilled it... something like a full quart extra if i remember correctly. after getting the oil level back to normal, they did another dyno run on it and it was at like 147 or something like that.
point of the story... i am always VERY careful not to overfill my oil after seeing the effect it can have.