We have a new feature coming in Patch 6.1 that’ll allow you to send out Tweets directly to your Twitter feed while playing World of Warcraft. It includes the ability to send out text-only Tweets; easily take, crop, and Tweet out in-game screenshots; and let your friends know about your recent accomplishments.It's not automated at all, and looks to be entirely under the player's control. If there is Twitter spam, that will be entirely the fault of the player.
Reaction, at least on the forums and in comments, seems to be fairly negative. At best, people feel it is a waste of resources. At worst, some people believe this heralds the decline of Western Civilization.
I take the opposite position. Now, I tried Twitter for a bit, and then dropped it, so this is a feature I will never use. However, there are a couple of positive results from Blizzard undertaking this.
First, consider the "This is EVE" trailer. If there is one lesson that MMOs should take from that trailer, it is that genuine player enthusiasm is the best way to market these games. Players visibly having fun playing these games, and getting excited over random things, are an enormously powerful tool for attracting new players or bringing back lapsed players.
Twitter integration is a easy way to expose genuine player activity to others. Since players are fully in control of their tweets, they will tweet things at an acceptable level. Or at least a level where they avoid everyone unfollowing them.
Second, this is a low stakes project for Blizzard devs to work with integrating with another company's service. At least one where the end user triggers the external service during gameplay. In many ways, the computer world is moving towards integration of services from many different companies, or even within the same company.
While not complex, there are always small things that go wrong with these things. You have to account for the other company behaving weirdly, or changing the rules on you. Developing best practices in a simple project like this can help with future projects. For example, Twitch.tv integration in future games.
I think that those two reasons--especially the marketing one--are good enough to make this project worthwhile.