Ive had the odd crash with Mavericks - something I never experienced before, with both Lion or Mountain Lion. Shutdowns take ages, and its usually while shutting down I get the odd crash. I shut down at the end of each day and its happened twice with my rMBP in the past week. The rMBP came with Mavericks pre-installed. I upgraded my MBA and Ive had one crash upon shutdown with that - my MBA has NEVER crashed since Ive had it from new. Co-incidence? The whole OS, although very nice, just seems a little flakey to me. I also find battery life worse then it was with Mountain Lion!