What's your test coverage?

For all of you with a production app with an existing user base, what's your test coverage?

I just launched our Public Beta for Learnify last week, and up until now our test coverage has been practically non-existent.

I'm now working on catching up with automated tests to make sure that major changes in the future don't cause any breaks, but obviously writing all these tests slows down our sprint cycle quite a bit.

What's your opinion on automated tests, and finding a balance between writing tests and sprint velocity?