I run my Mint on a 128GB super fast USB3 stick. Besides the OS I have a 115GB data partition on it that I use for my data and when I have to save the data of some poor guy who bricked his system. Then I need not attach another external device to store the saved data.
I do have 128GB USB 3.0 (the PNY on pic above), but no need. It's not my primary OS. I just play around with Linux. I just like exploring different platforms. Like right now I am listening to MP3s the "geeky" way. That is, via Raspberry Pi (Raspbian Wheezy OS) on SSH terminal.
Here is the actual desktop interface of Raspbian Wheezy OS. It's also a complete micro-computer system in a credit card sized board. The display is 1080p via HDMI.
And here's the micro computer. The $35 Raspberry Pi. It is powered by a mini USB connected to my PC.
It's a good idea to have a pocket-able OS like you do. But you still need to carry a computer to run it.
Yeah, they make fancy sticks these days. I got this one. It was relatively expensive but has an access time of 0.3ms. That is close to SSD speed. On the PNY I did not like this movable plastic cap. I took it of and use a real cover from some old PNY which fit.
Never use a stick to update Ubuntu. For most Linux distros, this is the worse option. I am more of an arch Linux user, where pacman -Syu will always work, but
I've never used that command before. I know it's possible however with
sudo apt-get dist-upgrade
but I do not remember exactly what I did, as that was a while ago on an Ubuntu server system, that now runs just plain Debian.
Either way, the stick is generally not the best way to go. It's more complicated and can lead to more.. complications.