if when trying to print you get the following error message in the cups web interface "/usr/libexec/cups/filter/foomatic-rip failed" like I did with my HP F4180 or like my buddy mythus who has a f HP photosmart D7100 series from #sabayon on irc. Don't worry too much your friend Jsizzle's got the medicine for ya

Here's what ya need to do
"emerge --sync && layman -S && emerge -u foomatic-filters foomatic-filters-ppds && /etc/init.d/cupsd restart"
Be sure your doing this as root. After this is all done you should be fine, if not reply to this post and I'll try to help ya out.
Hope this helps some folks,
Jsizzle