I am testing W10 on two boxes (i5/gen1 ASUS EP121 Tablet PC and i5/gen 3 Tower) since the official "final" version was delivered. Not yet perfect IMHO so it is not on my "main tablet pc" (i5 Lenovo Helix). The systems run stable even under heavy use (LR5, Netbeans etc) but currently the update frequency is a bit to high and the little problems are a bit to nagging to make it my production and/or main privat system. OTOH I have a well behaved and set up Win8.1 as production and privat systems so my pressure to change is low.
But with the progress done and the upcoming changes I will likely make the switch over the christmas hollidays. W10 has to many good elements over W8.1 (and a HUGE amount of them over W7 for my use cases) for me to ignore it and my "fewest amount of different OS" philosophie means just as I went Windows Phone I will also go Win10 for all client systems.