Lots of companies I respect were using it + open-source + great features and UI. Went for the hosted version, since it plays nice with Heroku. I like how they group together similar errors, give you the ability to mute events or mark them as solved. P.S. check out the Founder Stories feature we did on Sentry if you want to know how they started, its an awesome story.
If PagerDuty lets you notify devs when things go wrong, Sentry is what lets us know when they did. With centralized logs, quick system alerts and detailed overviews, it's a great addition to our system.
Sentry is amazing, most of our systems send their exceptions to sentry. We couldn't live without it and get a much better understanding of how our code is behaving in the wild. Plus it integrates with Github.