install (k)ubuntu on external hard drives

[roberto]

hello
i read on various documentation that it is possible to install
(k)ubuntu on an external USB HD, for example choosing the external
disk as the medium where to install GRUB and then the OS during the
great installation procedure of ubuntu systems;

my BIOS supports the boot from USB devices

here i'd like to know:
- if someone has successfully did it
- if the connection with the external hd is reliably fast
- which type of FS is better to use in the external drive
- other issue known by experienced users

thank you for suggestions

-- 
roberto
OS: GNU/Linux, Debian and Kubuntu