The group http://groups.google.com/group/sketch-users is the best place to report bugs and make improvements. A second method that will probably produce a slower response is email to sketch@frontiernet.net. We will try to respond, but can't promise. In any event, don't be offended if a reply is not forthcoming. We're just busy and will get to your suggestion eventually.
For bugs, attach a sketch
input file that causes the bad
behavior. Embed comments that explain what to look for in
the behavior of sketch
or its output.
A recommendation for improvement from one unknown person counts as one vote. We use overall vote tallies to decide what to do next as resources permit. We reserve the right to assign any number of votes to suggestions from people who have been helpful and supportive in the past.