What do you think of achievements?

Achievements are increasingly taking over the world of gaming and most major platforms now have some form of them, Xbox and Games For Windows Live have Gamerscore, Playstation has Trophies, and Steam games have achievements also.  What do you think of achievements?

Personally, I like them as they are often fun to do and encourage me to play a game in a manner that I might not have done.  Typically I'll briefly read over the list of achievements after I'm an hour or two into a game and do some of those during my first play through of a game and then once I'm finished it I'll do any other ones that seem fun that I haven't already done.  For a game that I'm really into I'll often get 600, 700, 800 + G just by doing what I consider fun achievements.

However, not all achievements are fun, there usually the nose-to-the-grindstone ones like "kill a trillion bad guys" or "reach level 100", so I just don't do those ones.  So even some games I'm really into and play regularly I won't have that many of the achievements.

So, what do you think of achievements?  Love em?  Hate em?  Are they ruining gaming?