Ask HN: What tool do you use for SAAS error tracking?

Hi, I built a SAAS webapp which sends me system error messages via e-mail message.

It's nice because I get to notice system errors the moment users encounter them, but it's a pain to manage. Also, in case of some errors (e.g. connection errors) I don't care if they happen once or twice a day or an hour. I only want to see them if they happen more often.

Any services that I could use to manage this? (my app's running on Python/GAE if it makes any difference)