Faster to have both the Gathering professions on your botting toon / account, get both herbs / mining done at same time.
I've only got one 80 so far and he's Herb/Mining for sure. I'm levelling a Druid to replace him with though since I kinda wanna transfer him to my legit account for PvP. Druids = crazy fast herb farming in Cata from flight form AND faster Tauren herb gathering! \o/ Also got a pally levelling in Northrend with skinning to feed one of my mains with LW, but probably use him for profit too since not many people seem to farm leather. On my current mining/herb farmer I mostly do one at a time, otherwise herbs OR mines will fill up your bags early, so it's less efficient. Saronite bars definitely BY FAR the most profitable thing for me so I tend to just mine more than herb. Once I level a main as alch/scribe I'll be doing lots of both though I think.
I have mining / herb on my bot account and on my main account I already had a JC and an Alchemist. For a while I was prospecting the Titanium Ore, smelting the saronite and making titansteel bars and flasks but now I can't really be bothered and just AH herbs, ores and eternals and vendor the saronite ore without even smelting it. I know I'm losing out on a thousand gold or so per full bags but I don't really need the gold and looking for as easy a life as possible.
Mining/JC on one character, Herb/Alchemy on another, you use the saronite bars to transmute to titanium bars, then send them back to the miner and make titansteel = goldmine On my other character I have skinning/LW which I use as he's a druid, also use the eternals from mining
