First off, please don't take this seriously. My intention is just to mock relationship sites in general through this section. I'm going to try to give some really messed up reasons why those couples would NEVER work out, even though I think some of them should... Ahh... I love playing the Devil's Advocate.

A: Tai and Sora: Ok... We've got the suicidal Tai on one side and we've got Sora on the other. Personally, I don't think this grouping would really work out. I don't know which will kill the other faster; Tai's suicidal tendencies or Sora trying to keep Tai out of trouble, only causing him to whack out and gun down a city block. (Would be interesting to see, though...)
B: Yamato and Mimi: Hmm... this would be rather... interesting, to say the least... until a tree appears and convinces Yamato that he has to kill Mimi to achieve true happiness. Now, on the Mimi side... I really don't think Mimi will be able to grow, behaviourally. Chances are, Yamato might actually treat Mimi much the same way he treated TK: Try to shelter them from the real world, only plunging yourself and the one you're "sheltering" into more trouble. Don't think it would work with Mimi... might have worked if it was Sora, though.
C: Izzy and Joe: ... Ack! I mean, I'm one for rights for homosexuals and all, but... Joe and Izzy?!! I can just see it now... "Izzy, I need to talk to you." "Affirmative, Joe. Just allow me a few milleseconds to close down this program." "No, it can wait..." "Prodigious!" As you can see, this might be a relationship, but Joe's too shy, and Izzy's too busy. In other words, they would never get together.
D: Takeru and Hikari: *singing* Oh, I wish I had Puppetmon's semi-automatic... No wait, that doesn't work with the music... Oh well... This is the one relationship that EVERYONE agrees upon. Everyone refuses to see those two with anyone else, not even Hikari with Daisuke (Davis). That conformity is the very thing that killed half my brain cells and caused me to create this site. I think that sums up my opinion on this relationship.
E: Yolei and Izzy: This is another one of my favorite relationships to hate. When you listen to the way when Yolei first met Izzy, I recall that the first phrase out of her mouth was "Wow, the legendary president of the computer club wants to talk to me." That, my friends, is called respect, not love. Then again, not very many of the characters in the world of Digimon really HAVE respect for anyone else, and it thus was misinterpreted (I KNOW I misspelled that, but I don't have a spellcheck right now) to be love.