We've only gotten 2 that I can remember in 4 years here. One was a regression in .Net 4.0 with high load hashtable inserts (which was previously fixed in 3.5 SP1) that they had to re-fix. The other was a SQL server issue in 2014 CTP1 we were running with an availability groups edge case on high volume/high latency secondaries.
Unless we're testing beta software, the MS stuff generally works and works very well. We of course work with them on feature requests that will make life better - some happen, some don't. I'm on the opinion you should try and have this relationship with any vendor or open source project. We're trying to make what we use better, and not for just us.
