Plone: redirecting logins to group-determined root page

Chat from #plone irc channel:

[6:00PM] dgroos
:  Hi I'm a teacher using plone.  Any (easy) way to make it so that  the page one is referred to upon logging in is determined by  this users group membership?

[6:05PM] dixond
:  dgroos: you probably need to customise login_next.cpy
[6:05PM] dixond: dgroos: it's in there that any redirect is traditionally done.

[6:06PM] dgroos
:  dixond: thanks.  is this fairly trivial or involved, do you estimate?

[6:08PM] Moo^_^
:  dgroos: it is easy

[6:09PM] dgroos
:  Thanks Moo^_^ and dixond, may the force be with you ;)

[6:09PM] Moo^_^
:  dgroos: http://collective-docs.plone.org/sessions/login.html

[6:11PM]dgroos
:  Moo^_^: thanks I'll note this for when the moment comes to implement it!