Unless you write some fancy javascript hooks, you can pretty much right
off back and forward buttons for intuitive navigation when you go to
frames.
However, every coding style has it's applications.
If you are building complex business applications that deal with tons
of data, complex data structures and workflows, frames are the best way
to go. Otherwise the users always complain about managing multiple
windows. Sure tabs make this less painful in the better browsers but
not much.
If you want to do frames be ready to write some rather complex JS to
make the application work properly.
If you cannot do JS for these sites, I would avoid frames. Frames
without JS are just too mundane un-intuitive. For example, when a user
navigates to the sub frame from a Google search result, they will not
get the entire frameset. This will result in the user only getting the
one frame. This can be prevented by the server checking if the user
requested the frameset within n seconds and if not send them the
frameset instead (complex). Also, JS can be written to search for the
frameset and redirect to the frameset as necessary (has a few tails but
is realtively easy to do)
JsD
