Some well written tutorials and how-tos for the Ubuntu user. Note that the author is careful to update things after each semiannual Ubuntu release. That alone makes them worth the price of admission (more, actually). Users of other Linuxes will also find it useful, according to how close their distribution is to Ubuntu.
For people new to Linux: read the advice on migrating to Ubuntu. The only thought I would add to that essay is to consider trying a virtual Linux box, either in addition to or instead of dual booting.