Power users- your Yosemite observations- functionality, reliability, good/bad

Fellow power users- please post your observations here, good and bad, regarding functionality, compatibility, reliability, usability, etc. that you have noticed in Yosemite.

I would like to hear things that would convince me to leave Mountain Lion, because so far I have not heard of any new features in Mavericks or Yosemite that I could not live without and that would compel me to want to go through the ordeal of migrating.

I'm a photographer, musician, and software developer who uses my Mac for many different things ranging from web development, iOS development, music production, etc. I've been on Mountain Lion forever now and love the stability and features, interface, etc. I could not be happier really.

I skipped Mavericks due to the removal of labels from the Finder, which I use to highlight things so they will visually stand out and make them easier to spot in a list of items. I could not think of any new features it offered that were compelling enough to make me sacrifice that.

So, aside from the new UI look-and-feel in Yosemite, what actual functionality improvements have any of you noticed? Have they improved anything related to audio production or photography workflows? Is there anything that would make my life easier as a web developer running PHPStorm here? Any improvements to the way the Terminal works?

How about memory usage and CPU performance? Do you find that running many apps at the same time is going to work better or worse in Yosemite than Mountain Lion? Does the system itself eat up even more background processes and slow things down, or is it more streamlined and efficient?

I don't have an SSD, but I've felt like Apple has been designing their system with more background disk access than it used to have, which is fine if you have a super-fast SSD, but on a hard-drive-based machine it might cause performance issues. Is that the case here? Or should a hard-drive based machine be fine?

Thanks.