Mac OS 0.10.3 and Photos (and iPhoto)
Tony Still 10.10.3 is a big (>2GB) update and seems to fix a lot of Yosemite's problems. It took a long time to download for me but that was within 24 hours of its release, hopefully it has improved now. It has markedly improved Bluetooth on my MacBook Pro and, apparently, improves WiFi to - I can't comment because I've not had any Yosemite-specific WiFi issues. In summary, this is the first time I've felt that Yosemite was sufficiently good quality for general release. As such, this is a good time to take the plunge.
If you use iPhoto you should note that installing 10.10.3 instantly terminates it. iPhoto will show with a no-entry sign and will refuse to run (it gave me an explanatory message that my version of iPhoto was incompatible with Yosemite and that I should go to the App Store and download the latest version - that's all nonsense and there is no version of any kind on the App Store now but hopefully Apple will have fixed the error message by now).
Instead of iPhoto there is the new Photos app. This looks good to me (disclaimer: I barely use iPhoto and don't expect to use Photos much either). When you start Photos, it offers to import your iPhoto library and then offers views of all your pictures that look a lot like the iPad version (the library seems to be updated in place, not duplicated). It also has editing tools like those on iOS (limited user control but good quality effects and do the basics quickly and efficiently). It includes a (new format, I believe) printed book creation tool.
The iCloud integration of Photos is, in my opinion, very good and resolves all my concerns. You can choose to enable any, all or none of 3 iCloud options:
* Keep all your pictures in iCloud
* Use Photo Stream as it already existed
* Create albums on iCloud for sharing with other people
If you use Aperture, this continues to work normally. I believe you can import an Aperture library into Photos but I haven't tried this. Aperture is on Death Row so you need to start thinking about the future; hopefully Photos will gain some more advanced tools but otherwise there's Lightroom or Affinity Photo, to name but two.