Hi Ricardo,
Our newest servers that have always had phpsuexec enabled from the beginning are running so wonderfully, that we had to start implementing this on our older servers. There was really no question about it in our minds.
It cannot be perfectly easy, although we wish it could be. This is a time when we wish there was an easy button.. most definitely.
Some scripts will need modifications in order to work correctly. Such as, some folders owned by nobody will need to be chowned by support, to your username instead. Sometimes this does not happen automatically as it should. So this is one common issue.. it happens often with the program Gallery.
If folders such as /images or /uploads have 777, then yes, you'll need to change them. There are not that many folders that would have such permissions. In a case if your client has maybe, all of his folders setup with those permissions.. well that shouldn't have been done in the first place.
That happens often if an installation is not working correctly and you've exhausted all methods to get it to work. Understandable.
However, the way I see it is- usually any given site has only a few applications installed that have such issues. It would only take a few minutes to change the permissions and in many cases you may not even have to make any changes. It just depends on what is installed.