lucy24 - 9:43 am on Nov 29, 2012 (gmt 0)
this directory has a .htaccess file that switches the rewrite engine off
The RewriteEngine is different from most things in Apache because it isn't inherited. Each individual htaccess files that uses mod_rewrite has to turn it on explicitly. Otherwise it's off.
Your with/without www redirect should be the very last redirect. On a vanilla html site, the second-to-last would be the rule to get rid of "index.html". The idea is to go from most specific to most general, so each rule only works on those requests that haven't already been handled in an earlier rule. Otherwise you could get multiple redirects.
If your whole site is built around a CMS so there are no "real" user-accessible directories, the trailing slash redirect is OK-- but make sure you haven't locked yourself out of any physical directories that you might need to visit! But the redirect shouldn't be necesssary in any case, since you don't have to redirect links that arrive in the wrong form.
How many URLs are involved? It may be safer to list them individually for the trailing-slash redirect. Use a pipe-separated list like
RewriteRule ^(preliminaryblahblah/(oneURL|notherURL|thirdURL))/$ http://www.example.com/$1
Unless there are potentially hundreds of 'em. You want to avoid redirecting to a 404 if possible.