Okay, my PM 5.0 seems to be working fine as well (no crashes, no problems, just as it was on Maverics) but I did notice one thing. I work with raw files. Usually, I edit them in Lightroom but sometimes, if I am really busy and do not have much time, I just crop and save (convert from RAW to JPEG) them through PM as it is much much faster then doing it with Lightroom. After update to Mac OS 10.10 I noticed, that it takes quite a lot more time than it did before - usually 100 photos was not a hassle, now it takes as much time as it would with Lightroom.
Working on MacBook Pro 15 Retina (i7 2.0 8GB ram), Yosemite 10.10 and PhotoMechanic 5, build 15800 (e6ecc1c).