The number of compiler bugs is a bit scary.
https://github.com/Araq/Nim/labels/High%20Priority
And also from what I've heard, the tooling isn't very good. Autocomplete isn't context sensitive and using GDB to resolve a variable like "foo" actually becomes "foo_randomnumber".
This is actually one of the things that keeps turning me away each time I try Nim. All software has bugs, got it, but in my mind a language nearing 1.0 should squash some of that list (or remove/feature gate things causing them) before even thinking about a 1.0 IMO.
I see similar lists for GCC when a branch is underway. I'm actually impressed with the number of active contributors, and I find the design very compelling. I'll be keeping an eye on this project.