Note that my shammies are no longer melee. I ran them melee/enhancement up through the 50s because gear for elemental shammies SUCKS until you hit outlands (unless you wear all cloth...ewww). I switched to elemental at 53 after running Sunken Temple. Shammies/rogues are pretty good at melee but to spec/gear for DPS means you have crappy tanking ability (and, thus, get owned by bosses fairly often).

When I start my druid team, they'll be melee up through the 50s due to the itemization issues much like shammies have pre-BC. Should be fun, especially since I can bear one up for tanking without changing gear.

[edit] It should be also noted that you don't strictly NEED to run instances to level fast, though you do get good loot to help speed leveling/questing if you do.