Yes I am a big fan of qemu.

I have a pendrive with a booting Damn Small Linux image, unlike most distros on a pen drive this one does not require me to reboot the machine and depend on the bios being able to boot from a USB device.

I simply have a batch file (or shell script if I am launching from a Linux host) that launches qemu and then loads the DSL image within. Nothing needs to be done to the host for this to happen and about 80% of the time it can either do a Bridged or NAT style network connection to get to the outside world. Works on Windows and Linux hosts (not got it working on a mac yet)

I have mine preconfigured with my mail accounts, VPN access to our office, X forwarding over an ssh tunnel to my home machine etc etc. So even when I don't have my laptop with me I have access to just about everything I could need. The only requirement on the host end is at least 128MB memory and preferably USB2, but if I was in a fix I could boot it to init 3 with a lot less.

Super useful tool for the cost of a 256MB memory stick (it would fit on a 128) gives me the same computing environment wherever I go and REALLY freaks out some of my clients !

P.S if you do this you need to make sure that if you lose the pendrive the finder does not have access to all of your remote login credentials, don't save or store any passwords on it etc...