As a veteran of countless MMOG launches and betas, I've come to realize that when problems inevitably surface, a transparent and honest approach will garner the most respect from your game's community.
Most MMOs will encounter at least one or two major hiccups during their launch. Even World of Warcraft had a very shaky start. Sometimes these problems will only affect a certain portion of players, and so a developer may be inclined not address the issue as loudly. But a forum post buried in a sea of topics is usually not enough.
The problem with addressing issues on twitter, blogs, or even forum posts is that angry players are likely to voice their complaint before reading these posts. It's best to prominently place messages on the launcher. It may seem like a bad move to "put your worst foot forward" as it were, but the truth is that players for whom the game works are not likely to care, and posting it on the launcher means that prospective customers will not see the message.
These posts should be as informative, offering workarounds if possible, and should channel players that are experiencing problems to the right area of your forums or site. I've found that most players are not satisfied when posts are made that read something like: "We are aware there is a problem and are currently working to fix it, but we have no ETA."
If there is a problem with a downed router somewhere, say so. If there is a problem with the way a patch was implemented, say so. Players will respect and appreciate your honesty and additional information.
For instance, in Champions Online's recent launch, a slip up caused a lengthy outage. But rather than a generic, "we're working on it" post, Awen of Cryptic confessed that a new member of the team had made a crucial mistake, adding that it would be resolved soon. The community's response was relatively positive. Yet when Cryptic neglected to sufficiently address the technical issues that prevented hundreds of players from progressing past the launcher, their boards were flooded with angry posts. This can hurt a game's launch as prospective customers are likely to visit its forums before making their decision on whether or not to purchase.
A good community is essential to an MMOG's success, and it's all about how you manage it. The community manager is a position that has gained importance in recent years. It is important to establish a good rapport with your players, but be careful not to sound condescending in posts, particularly those made addressing downtimes or other technical trouble.
Avoid "sounding cute" to angry customers. Don't begin posts with greetings like "Good Morning Heroes!" when dealing with these sort of problems. Remember that you are speaking to angry customers, who have every right to be disappointed by the fact that your company has in some way not delivered on a promised service, and should be treated as such. There is a time and a place for everything.
The nature of the internet and games does not typically engender respect. But if you want respect from your players, its best to respect them first.