It's interesting to note that the above 2 responses refer to "surfaces" or "SP3/SP4/S3." To be clear, I only spoke about the SP4, not the other surface devices.
I find it hard to believe that that above 2 posters used their SP4s for mission critical purposes during the period prior to the February and March 2016 fixes and didn't run into any problems, particularly if they were doing cutting edge things. At the vey least, I'm sure they experienced multiple video driver crashes during that time frame. I also suspect that they had to resuscitate their SP4s using the secret 2 finger salute a few times. How quickly we forget...
SP3, S3, SP4 (SP4 predominantly since release). All work perfectly. The only issues (as in one which had a tangible effect) I've had have been as a result of being on fast track insiders and almost entirely related to inking in desktop onenote. I bought my surfaces for university, specifically the pen capabilities. They have been used since day one, and were on the fast track insider program the moment it was available. During term time, they get used all day every day, and are a charm to use. You will find that there are many members on this forum using their sp4 for their job, and get on just great.