I do both iOS and Android development thus I have a MacBook Pro has my main development device. I have had one for the last 3 years. Since upgrading to Yosemite it has become the least stable development box I have worked on in a long time.
I leave the machine on and lock / put it to sleep when I am away from my desk. This may be going to a meeting, going to lunch or home for the evening. When I come back from lunch there is a very good chance, 2 out of 5 days, that the machine has rebooted. This also may happen during the day when I am actively working on the machine but that is pretty rare. The sleep cycle seems to be the main trigger.
This is an upper end machine with an SSD drive so the reboot does not take too long but it does interrupt my day and it may happen a couple of times a day, when I come in, after lunch and then maybe after a meeting. Yes, all the programs restart but they don't show up in the same position or with the same data showing. Sublime text appears on screen 1 instead of screen 2. Finder does not have the same tabs open. Chrome might be annoyed in some manner. I will not have the tabs in iTerm on the same directories.
This was never a problem in the past. The MacBook just worked. Now it reboots and has issues with DNS getting lost part way through the day as well. Ping will not find a machine but NSLookup will.
I also have a Dell PC that is used for my Windows activities running Windows 8.1. I leave Outlook, Hipchat, Sublime Text, Chrome and a few other things running on it as well. I do a lot of my graphics work on that machine because Paint.NET is free and pretty darn full featured. We also use TFS for version control and I do that work on that machine along with anything I need to do in Visual Studio including C#. I don't have a massive love for Windows but at least that machine is only rebooting when it needs to do updates, which does occur too often for an OS, but otherwise it is there ready to go.
iOS has become less stable as well. I think Apple needs to stagger the releases instead of trying to do MacOS, iOS and iOS hardware release all at the same time. I bet their QA department is hammered during that yearly cycle and it is really starting to show. I love new and exciting things but they need to be stable. Right now Yosemite is not stable and is highly annoying.