I have installed the VM's on an SD card within a hidden Truecrypt volume so if they want to take a look they can. I've never been fully sure of what is left on a computer when using the TBB or another OS like Whonix but I am fairly certain it wouldn't be enough to secure a conviction, yes it may show evidence that the TBB has been used but so what, that doesn't constitute a crime. Having spoken at length to some of the biggest tech heads on here I was advised against tails, don't ask me for the detailed rationale again because I purged the emails but I think any system comes with its +s and -s, at the end of the day using a system like Whonix or Qubes is still going to make you a fuck load more secure than just firing up the TBB on your Windows 7 machine.