Ok, I'v took your replies in to consideration, and thought about it. And this is what I think; Alliances of two people are fair game. Alliances over two people are overkill and unfair. With a 2 player alliance, the solo player still has a chance of beating them with cunning tactics. But with a 3+ alliance, the chances drop tremendously, especially if they have diamond tools or armour.
As others have said, I actually do like alliances, when it's only two players. I'v had a few experiences where i'm hiding in the tree near spawn, spying on a two player alliance. What I don't like is when they sit at the cornucopia for the enitre game, just waiting for the chests to refill so they can keep getting better and better items.
I may think about trying out allying with someone for a game. I'v tried it once, and I didn't like it so much, just gives you more weight to carry (so to speak)
Conclusion: Two player allies are cool, when they don't camp at the cornucopia all game. 4-8 player allies are NOT cool, and it's ruining the game for solo players.