Sorry was 8 years ... ClickOnce refused to launch on over 2000 machines when they removed download prompting from IE9. This sits between the .net framework and the IE team, neither of which would take responsibility for fixing. Eventually we got a registry fix out of them from bottom line support which turned download prompting back on which was removed from the IE UI but still left in there. The registry fix we had to deploy to hundreds of clients and had a massive support cost. This is still broken in IE11. It was reported on an IE9 beta.
Pain points: large project performance, high concurrency projects, IDE reliability, cost, odd time sinks, bugs in the framework, lack of automation possibility for a vast number of project types (try building VSTO applications on a CI server), deprecations (WWF/WCF changes, AppFabric, Velocity etc) all sorts.