Just for the sake of comparison... lets compare
Digimon:
Protagonists get one Digimon a piece.
They all talk
They inhabit the Digital World and cross into Earth.
They "Digivolve" to higher levels, then revert (including fusion of Two Digimon or Digimon and Humans)
Digimon depicts death
Antagonists are evil powered Digimon who look to maim and kill.
Digimon and partners are paired for specific reason/destiny.
Pokemon on the other hand, has not had a different forumla since day one. Not saying its a bad thing whatsoever, dont fix whats not broken, but the series has always been about Ash going to a different region, making new friends, and battling Team Rocket. Which Im content with, but when you get down to it Digimon and Pokemon are really nothing alike.
But for the counterargument, ill compare similarites:
Digimon vs. Pokemon (Digital Monsters vs. Pocket Monsters)
Digivice vs. Pokeball (?) (Device needed to make Digimon evolve vs. Storage container for Pokemon)
Digivolve vs. Evolve (Digimon go to higher levels, then revert back down vs. permanent Evolution)
Tai vs. Ash (Pretty much identical)
Thats about it as far as similarities I can come up with. Which basically amounts to nothing.