One "tip" that I learned is to set your bit depth using a scrap of the same wood your cabinet sides are made of.
Cut a slot down one side of the scrap.
Here's the "tip":
Now, flip the scrap over and check the bit depth against the slot you cut. If you're dead center, the bit will hit EXACTLY in the center of the slot you just cut.
An expansion on the "tip":
I found that t-molding "wants" a 3/32" slot cutter. most people use a slightly smaller 1/16" slot cutter, because it's more readily available. If you're using a 1/16th, center it as best you can using the method above. Then route the slot in your cabinet sides. Flip the side over, and RE-ROUTE the slot without moving the bit. You'll end up with a PERFECTLY centered slot almost exactly the right size.
Hope this helps someone.