Digimon and Pokemon are very similar in some areas, but they have a lot more differences than similarities. Basically the only similarities are the 'raising monsters' thing and evolving them, oh yeah, and introducing new monsters every season. But the differences are more numerous. For example, there's the whole talking thing that was mentioned in this thread, de-evolving(also mentioned), and only digimon per character(also mentioned). There's also other differences, like the fact that only a chosen few recieve digimon, whereas basically everyone gets a pokemon, every season of digimon after the first has its own special gimick that sets it aside from the others(season 2: armor-digivolution, season 3: digi-modify cards, season 4: spirit evolution, and so on), whereas pokemon has been, for the most part, the same for every season(until recent ones where DNA splicer and Mega Evolution were added[which I personally believe those really were ripped off of digimon's forms of fusion and digivolution. Seriously, how is Mega Evolution not the same as digivolution aside from names? Both require a bond between the human and the monster, and both return to their previous form after the battle is over]), and finally, digimon, while having different characters each season, always has one main character that wears goggles, whereas Pokemon has had the exact same main charatcer for every season, while changing those he travels with. So digimon is NOT an exact copy of Pokemon, it just used a similar basic idea, just like Dragon Ball and Ranma 1/2 both use martial arts and ki manipulation, and Avatar: The Last Airbender and Xiaolin Showdown used element manipulation and chi. Just because Pokemon came first, doesn't mean digimon is a rip-off.
Don't get me wrong, I love Pokemon, and I never really watched digimon while it was on tv, but I did watch it eventually and I love it just as much as Pokemon. My personal favorite seasons are Tamers and Frontier(aside from Adventure 01). I liked digi-modify and spirit evolution. As for Pokemon, my favorite era was when Ash was in the Hoenn region. Deoxys remains my favorite Pokemon while Guilmon is my favorite Digimon.
As for Digimon looking like Pokemon, I'd chalk that one up as coincidence(and by the way, Guilmon looks a lot more like Charmeleon than Agumon. Aside from the markings on Guilmon's body, the biggest difference is the bat ears).
And does anyone even bother with the trading cards? Sure they're alright to collect, but Ijust stick them in a box to collect dust because there's not really much you can do with them. Pretending to have a Digimon or Pokemon battle with cards isn' nearly as entertaining as doing it in a game.
As for the games, Digimon World was okay. I wouldn't go as far as calling it the best game in the world, but when it comes to games in its genre, it' among the top three in my book, right behind the main Pokemon games. Also, did anyone here actually LIKE the mystery dungeon games? I thought it was okay, but not worth even a little bit of game time.
Oh yeah, and a crossover between the two wouldn't really be all that bad if it's done right. At least that's what I think.
All the similarities and differences I mentioned, as well as others, can be found here:
http://digimon.wikia.com/wiki/Fan:Digimo...k%C3%A9mon
And yes, I know Wikipedia isn't exactly the best source, but I know for a fact that this information is reliable(having playing many of their games and watched their animes).