T-Mobile Sidekick users are in great danger (pun intended) of losing all the personal data on their Sidekick phones if they haven't already lost it.
On Friday T-Mobile posted an official statement apologizing for the recent Sidekick data service disruption. On top of that Microsoft and Danger said in the statement that personal information stored on your Sidekick - such as contacts, calendar entries, to-do lists or photos - that is no longer on your Sidekick has almost certainly been lost as a result of a server failure at Microsoft/Danger.
Today Microsoft and T-Mobile plan to issue another statement about the status of the remaining issues caused by the service disruption including data recovery efforts.
If you still have your data on your Sidekick you should not reset it by removing the battery or letting your battery drain completely, as any personal content that currently resides on your device will be lost. What you should have already done anyway is backup your data, but apparently this is not an easy option on the Sidekick.
I am not a Sidekick user, but the Hiptop3 blog posted instructions for saving your contacts that requires manually emailing each contact stored in the Sidekick - sick! In contrast Apple's iTunes backs up your complete iPhone data for you.

This data loss is a huge disaster for everybody involved, especially Sidekick customers. An unconfirmed rumor on Hiptop3 points the finger towards an outsourced SAN upgrade. Apparently nobody thought about making a data backup before the upgrade - unbelievable. We will see how open Microsoft is about what has really happened later today. Reading comments from some Sidekick owners shows that many didn't even know that Danger has been owned by Microsoft for a year. Now they know!

T-Mobile is certainly not happy about this image damaging situation especially as they are about to launch something big dubbed Project Dark soon.
For Microsoft this is just another very bad thing that adds to the weird stories around Project Pink and Danger.