How many still exist? Pretty much all of them. I have yet to hear of a definitive fix for all but a couple of problems that have existed at launch, and the real big ones are still out there.
Many of us have discovered workarounds for some of the issues, but Connected Sleep is nowhere close to working as advertised, the CPU driver does not throttle back quickly enough to conserve power, The GPU driver still crashes regularly (if somewhat infrequently in most cases), the typecover has 3-4 different issues (hanging start, causing phantom drain while the machine is off among them), the Dock will not sync two 4k montors at any refresh rate, and the pen makes jagged diagonal lines are a few examples.
3 months into what we might presume is a 12 month premiere lifecycle, I expect that means that very, very few actual bugs in the hardware - such as the typecover problems, the phantom power drains, the poor power management (and hence battery life), and the dock problems will never be fixed. In three months (if not by the end of this month) the team will be pulled to work entirely on the SP5 and anything which remains wrong with the SP4 will be a permanent condition. (Note, I hope MS proves me wrong, but I've settled in that what I have is all that will ever work, and that Panos is a liar)
Windows 10 also has a laundry list of bugs, but that will follow you no matter which W10 PC you get.