Heh.
I've given presentations using both KPresenter and OpenOffice.org's Presenter. Unless you desperately need to make your presentation into a cartoon they both are at least as good as PowerPoint.
But if turning your presentation into a cartoon is what you really want, the GIMP works wonderfully. And both KPresenter and OO.o Presenter both support importing EPS files from the GIMP.
Now if you are serious about building a quality presentation...
MagicPoint rocks.
People who don't know anything about Linux software should refrain from commenting on it.
The current homepage of magicpoint (also includes some sample presentations here and here)
Gimp is fine, and I use it all the time, but it is not Macromedia Fireworks. Again, you get what you pay for.
OOOH Gimp and Open Office are somehow secretive to only you, except, except.... I use it everyday on My 10 computers running Edubuntu... and they are crap but good for basic crap... so don't defend crap unless crap is truly what you love.