Having finished grinding out my Argent Dawn reps went ahead and dropped Herbalism which I've had with Alchemy for forever. But for WotLK made a tough decision and picked up Mining. So started leveling Mining up to keep rolling with getting things done vs playing around and killing time with Scourge Invasion events just being focused.
So far have Mining up to just over 200. When I'm done will have my lvl 70 Hunter drop Mining for Herbalism, so its a character profession switch mostly. Almost all my time is spent on my Paladin and my Hunter is just for fun times and laid back activity. Since I'm going to need to Mine a bit of Ore for some Plate crafting needs, Transmutations (Titansteel) and more (AH profiting) I prefer to have it on the character I play all the time to drain Northrend of precious Ore farming which I'm relatively good at.
Considering also having Mining with Alchemy I can burn 2 cooldowns in WotLK making Titanium Bar with Alchemy which seem rare to find Mining based on my time in Beta. As well making Titansteel Bar with Mining which I also figure will be expensive and likely profitable. As well the HP buff from Mining will benefit me more as a Tank anyway vs Herbalism which will have my Hunter pickup and level after leveling up mining to maintain my Alchemy needs. I've never found I use the Herbalism buff much anyway mostly forget its even there.
Edit: Completed leveling up Mining to 375 on my Paladin.