I spent Saturday finally putting to action an idea I'd been playing with for awhile - picking Outlands clean. I started in SMV and flew over every node in every area, picking everything in site. Skipped nothing (well except for a mana thistle in Nagrand which was surrounded by 4 of those shadow prist guys and another in Nagrand right at the base of those fel cannons).
All told, it took more than 4, but less than 5 hours to complete - and I took some time to do the daily cooking, fishing and the SSO Nagrand, HP, and Netherstorm dailies. SMV and HP took the longest, but mostly because I didn't have a set search pattern unlike Terrokar and Zangarmarsh. Thank Blizzard for epic flight form!
I'd definately say it was worth it as I completely restocked my supplies of pots/elixirs/flasks I used, gave a goodly amount to the guild, and still had a myriad of pots and elixirs to sell on the AH. Among the 'special' drops, I got roughly 15 motes of mana/shadow, 25 motes of life and 8 fel lotuses.
Doing all the zones in one swoop has the advantage of letting you get into the rhythm of farming. It also gives you herbs you may not actively seek out because you don't need them, but perhaps your guild or economy does. But it does take some time and obviously keeps you from other tasks. I may try breaking it up into a zone or two a day.