Ok then well I will share my humble thoughts on the subject here regarding sorting posts by upvote.
Pros: good for question and answer sites like stack exchange sites. It enables the best answers to move to the top of the topic so people can find the answer to the question they are looking for quickly. Consequently, the forum becomes a knowledge base, where anyone searching for the previous question can refer to that site and find the answer easily (without reading all the posts). There are a number of wordpress forum sites which specialize in this: SabaiDiscuss, CM answers, Q&A, Design wall etc.
To get an idea of the popularity of Q&A type sites maybe look at the views of these posts: http://meta.stackexchange.com/search?q=clones
If Simplepress could only have a way of sorting posts by upvote then it would have all the functionality of these Q&A sites and much more. It could draw clients that would otherwise sign up to those sites. Maybe it would be a good idea to have a plugin called “Q&A plugin” or something which would enable sorting and perhaps reputation based on upvote. That would also help market the Simplepress to people specifically looking for Q&A type sites.
Cons: Of course sorting by upvote mixes up the chronology of the discussion and isn’t best for these type of forums.