Done this job for 23 year now, and probably had this phenomena for 23 years too.
I started with Aldus Persuasion (still better than the current version of Powerpoint), moved on to Powerpoint once it was released (for Mac only at the time) and also had to use Lotus Freelance for certain clients.
It wasn't too bad when you only had black & white, plus some patterns, but adding colour and 'automated' diagramming makes everyone think they're a Powerpoint expert.
It's simple: if it's your own presentation, you just keep a few keywords/pictures on the slide to prompt your speech. However a lot of the time we see companies who want to put the reporting info from 10 divisions, 10 functions, and 20 Directors into a Powerpoint slideshow so that they can 'talk about it'
They're paying me (well), but I still try to advise them to do a hand-out pack/report with the detail in and just do 10-20 slides for the slideshow. Sometimes it works, mostly it doesn't
I suppose that's why I'm still in business - although I've expanded from just MS Office to a complete document production/analyst service, and why there are more companies popping up (
e.g. M62) who'll take your 300 slides and condense them into something usable, and supply you with speaker notes to go along with it.