For grouping I would suggest filling the last 3 spots with friends or a PUG - at 70 I maxed out my shaman gear wise and then started playing my hunter again - I ran my own ZA and filled the other 8 slots with friends/PUGs - I was the healer on my shaman and DPS with my hunter - That paticular set up the hunter follows the shaman and I spam one key which randomly fired my shots, cool downs, beastial wrath, ect and over a couple of weeks my hunter was also maxed out with ZA gear.

When WOTLK came out I intended to level my hunter and shaman togather but I found my shaman getting ahead because I was often called to heal for a group that only had 1 spot open and I wanted to see the new content so my shaman got to 74 while my hunter remained at 73. After that I decided to try 5 boxing shamans - lately what I've been doing is running my 4 lower level shamans (L71 now) with a tank - so far I've only tried this with a DK pug and it didn't go so well - we wiped a lot since my shammies are elemental, but with some practice or one being resto I can do it.

-Clov