As much as World of Warcraft is an excellent MMO video game, there are a few annoying things about it simply because if its very nature. MMORPGs deal with real people and it is not totally impossible that you will meet people who will either PK you or disturb your raiding sessions.

Given that premise, it is a great thing that Blizzard decided to implement an in-game tool that allows players to ignore others players. However, the more intriguing thing here is why there's a limit to this "ignore list". Is it a technical issue? Or is it something else? Blizzard forum moderator Aeus explained:

Since this is a massive multi-player game, we really value the social aspect of it. It is hardly ever necessary to permanently have someone in your ignore list and I think limiting the slots will make every player a little more conscious of whom they're blocking and why and to not turn this game into a FPS.