I use various versions of FOG Trunk at six different sites at work, it works with minimal issues. When we have issues, I report them and the developers work on a fix and normally have a fix in a few hours, a few days max. I also run FOG Trunk at home. Several people here who frequent the forums run FOG Trunk in a production environment too. I consider FOG Trunk to be quite stable and well worth the move simply for the vast improvements and feature implementations, not to mention the new client as well.
We really need more than “It doesn’t work right / it’s slow” in order to help you.
For the web UI issues, there’s an area in FOG Configuration -> Log Viewer -> Apache error logs that are needed to troubleshoot that problem. You may also output the Apache errors via CLI but I can’t give you a command for that because you didn’t tell us your OS. For the PHP5 issue, there is an installation log that shows the exact errors, these errors will also show up in the system logs, too… but again… we need the OS version to give you a command for that.