I have a pretty new IN-100 that I've only been running for about 2 months...
The "break-in" period for mine seemed to take about a week before I could let it run for a full day without having to adjust it. Just make sure you start with the label that says "open" directly over the Arrow. Every 30 minutes or so, slowly turn the top pipe towards the "closed" label, rinse and repeat until your bubbles are close to the lip of the skimmate cup. Once you get here you can really fine tune how "wet" or "dry" your skimmate is by just barely turning the pipe one way or the other. Just remember: turning your pipe closer to closed causes the bubbles to rise higher in the colomn. So if it is filling up too fast, you have to turn it down some.
I've also learned that any time I change a filter sock or do a water change, just to unplug the whole thing, it seems to go crazy like you've said after ANYTHING in the tank changes just a tiny bit.
After it was all said and done, I'm very happy with mine: it skimm's the crap out of my tank and is very quiet. Just be slow and patient with the "fine tunning" and I'm sure it will run great for you, too.
-brandon