We're using it at http://sprint.ly/ . In general, I like it.

I wish...

  - I could search w/ meaningful results
  - I could group by exception type.
  - I had a better method of seeing the different input data that caused the exception (without next/next/nexting).
  - there were lots more information around my source code.

I could probably come up with a few more if I were pressed to. All that said, we'll continue to pay for the service b/c its useful to our business.