Also just came across this:
In Plesk 9.* under the domains 'Web Hosting Settings' icon you now have the ability to activate 'Fast CGI Application' for 'PHP Support' (instead of the normal 'Apache module' option). Do this and also tick the FastCGI support tickbox if required (i suggest to just do it anyway).
This will now stop the server writing files as apache:apache and instead write the files as ftpowner:psacln instead. So now you have full control over your files and can develop using Joomla in a PLESK system.
As usual you may have to '777' some directories which can be easily done through ftp.
forum.joomla.org/viewtopic.php?f=429&t=348238&start=0