I've just finished my sermon PowerPoint for tomorrow morning. We are doing a sermon series based on the Mission Shaped Introduction course by Fresh Expressions. This is intended to be run over two hours, I have to modify the content to work in 15 to 20 minutes! The course comes with PowerPoint presentations for each session which I need to modify.
Key thing - you don't have a slide because the concept is easy to illustrate. You don't have a slide because you can find lots of pictures. You don't have a slide because you had a really cool idea. You need slides to reinforce points and sometimes to help resolve complexity. You should have slides for the things that you want people to remember.
This helps with which slides to take out when you realise that there are too many!