When you reboot the ESXi 5.0 host, I have found it to be frustrating that by default, you can often wind up with virtual machines that are forcibly powered off, rather than gracefully shut down.
Amazing, this simple (admittedly somewhat strange) fix actually seems to work.
VMware KB Article 1008182, Virtual machines do not shut down gracefully, and optionally,
VMware KB Article 1744, Gracefully Shutting Down a Windows Guest When the Virtual Machine Powers Off.
Yes, technically, you very much should login to the console of each VM, and verify a clean shutdown. But in a lab, or even in production, you may get sloppy and forget.
Perhaps you have a piece of software that monitors your UPS for power failure signals, shutting down the ESXi host itself. Wouldn't you also want the cleanest possible unattended automatic shutdown for all your precious VMs as well, before the hypervisor goes down and the system is powered off? Consider setting your BIOS for automatic power up after power is restored, and set your VMs to autostart, so your distruption due to power outages is minimized.
Consider making a comment here below, to let us know if this works for you too!