I'm running Ubuntu 12.04 in Virtualbox under a Linux Mint 13 host, and I noticed that powering off the machine (instead of shutting it down) took more than 42 minutes. I chose to power off the virtual machine because it had become totally unresponsive. The progress bar on the "powering off" notification is stuck at around 50%. What is the usual cause of this problem (if any is known)?
(I'll admit that I didn't look at any of the log files before posting this question - I'll try to add this information as soon as possible. The log files may contain relevant information, but I haven't yet found the relevant files.)
Recently, on September 1, 2013, I encountered a very similar problem on a Windows 8 host machine with a Linux Mint guest machine. Now it's stuck at 14% instead of 50%, and the estimated time remaining is more than 2 hours.