Ghost's explanation doesn't really point to how points is a useless method of ranking, so I will briefly.
First off all, points only show how many you can still spend, not how much you have invested in games. It doesn't really make sense that if I join a game then the relative ranking will go down.
Secondly, it doesn't reflect the relative skill of other players. I've played alot of organised games with really good players for example, its only been 5

to enter. They may have been alot harder to win than most games on this site, but the points just didn't reflect that.
Third, you can lose points. Say for example, I play fifty 5 point buy-in games wta and win them all. Thats crazy. I have won 50 games straight. That would win me 1750

. I think it would be safe to say that I am amazing. Now if I joined a super high pot game for 1650

, and then lost, my record would be 50 wins and one loss (or even a survive in wta) but my point total would reflect me having the same rank as someone with 50 losses. Indeed, someone with 1 win, 50 losses would have a higher rank than me.
Fourth- Points inflation. The nature of the game means that if you are of moderate ability your point total should go up. Lots of bad players join, deposit points, then cd or lose. Good players that hang around should always get more points. What does this mean practically? Well take my 50 win example. He could go undefeated. But if he takes a break from the site, after a while tons of people will have passed him just because he isn't keeping up. Also, it means that as the site ages the top players will have point totals (this is something we see now) that are basically unacheiveable, even by really good players.
Fifth, points replenish themselves. So you could lose a bunch of games and still be back at 100. Thus you can play the system by betting the house. Someone who plays high risk will probably have a high point variance, but will at some point have a really high total, reflecting not his skill, but his luck of recent days.
Anyways, thats all I can think of right now. But I think it should be clear to everyone that points are meaningless except to control how many games new players join.