I've experienced a lot of crashes since 10.9.3 on a late 2013 rMBP, mostly when sleeping/waking the device. Also, my WiFi is randomly disconnecting all the time since the update. Before the update I never had any issues. I love the hardware and the OS a lot, but I never had any crashes with my ugly Lenovo, so I'm currently thinking about switching back to Lenovo
I don't get the WiFi disconnects, but 10.9.3 has stopped being able to automatically connect to WiFi.
Wake up Macbook from sleep and find WiFi disconnected. Click icon, see only a couple of SSIDs, click the one I want, get the "unable to connect dialog". Click icon again and wait for refresh; now see a much longer list of SSIDs. Click the same one that it couldn't connect to before and it finally connects.