Hi there. I wan to install a distribution on a USB flash drive so i can use it anywhere I go(Not a Live USB). I will need VIM as my editor, and a web browser. The rest is not that important. There are many options, from Crunchbang to Arch and many others. I have couple of requirements, though:

1. CPU agnostic (so i could boot the the distro regardless of the CPU type the machine is running on,weather its X86, X64 or other processors like i676)

2. Lightweight (Short bootup/poweroff time, light on RAM, fast window management)

3. Hustle free (Easy installation process, including distribution itself, as well as additional applications, drivers, low maintenance (wifi compatible since i will be using the distro on laptops mainly))

4. Persistent memory (So I could save documents and do changes to the system)

I am an open mind person, so open to any suggestions. Thank you!

I like Knoppix; it does everything you specify, though I'm sure many others do too.

I've just downloaded the latest 7.4 Knoppix. Ran it in VirtualBox. First impressions are that its quite slow, maybe just because its VM? Tryied to install it on a flash drive from VM and it gave me an error. I guess i have to run it LIVE from a DVD.

Hmm, well mine runs acceptably well off a USB, but maybe my expectations are lower.
Here are 6 other recommendations, courtesy of Linux Magazine:
4MLinux
Tiny Core
SystemRescueCd
Slacko Puppy
Clonezilla
Slax