I was an old foldershare user, so all my sync folders were under a folder called foldershare. I just moved that folder into the dropbox folder, and it keeps them all fine, I never bothered doing anything different with them. So it looks like this

\dropbox\foldershare\whatever
\dropbox\foldershare\and so on

I've never had a problem with any reduction of speed with dropbox, foldershare, or the live product. They run way in the background, and seem to step back when the machine is needed for other things.