The most common defect I find with Scanahand generated fonts is the baseline alignment. More often than not, my fonts come out like this, which might be OK for a handwriting font, but is not so good for copperplate lettering or machine-cut fonts.
One way of solving this problem would be to have a manual generation mode, which would stop to show each glyph before it is generated, and allow the user to manually adjust the position by clicking some buttons.
There could also be an eraser to clean any stray pixels that were not supposed to be part of the glyph.
