Most of the alts that I've created since the Cataclysm have a gathering profession of some sort, sometimes paired with a matching crafting profession. I'm finding it quite noticeable how gathering has been changed in the revamped old world.
Mining has probably undergone the biggest changes. It used to be... not really difficult, but somewhat messy, as different ores with different skill requirements were all over the place. I'm sure that everyone who's ever levelled a miner before the Cataclysm knows the feeling of finding a random iron or mithril node in what's otherwise a low-level zone and then doing a dejected /cry emote next to it because you didn't actually have sufficient gathering skill to collect the shinies. Or maybe that was just me. Either way, give me a break, I only just started on tin! And who ever thought that Stonetalon Mountains should have mithril nodes in it anyway?
This could sometimes be frustrating, but it also made ores very valuable because it was hard to do any focused gathering. Thousand Needles used to be considered a good place to mine iron for example, but it had just as much - if not more - copper and tin nodes taking up space, and nodes were generally pretty sparse to begin with, at least compared to something like herb spawn points.
Well, let's just say, the Cataclysm changed that as well. There are still "transitional" zones where you'll find more than one type of ore (for example tin and iron in the Wetlands), but never more than two different types, not counting the rare spawns like gold and silver. A lot of zones however have been "purified" completely. Western Plaguelands? All iron, all the time. Badlands? Same with mithril. Searing Gorge? Also nothing but mithril. (I thought that was funny actually, considering how all the outposts are called Thorium something-or-other. It doesn't quite add up now.) In addition, the number of ore nodes in general struck me as having been increased a lot and it's now more on par with herbs. I don't have any hard data to back this up, but it really was very noticeable. For example I'd go to an ogre cave in the Badlands and find four or five nodes right around the entrance, then another five inside, and by the time I came back out again everything outside had already respawned again as well. To someone who's used to ore, especially certain types, being a rare and precious commodity, that's simply insane.
It shows on the auction house as well, with many ores only going for a couple of silver per piece these days. I reckon that levelling a crafting profession that depends on mining, and especially on particular kinds of ores (*cough* blacksmithing *cough*), must be a lot easier these days than it used to be, even without any nerfs to the actual crafting requirements. I guess that's a good thing, though I have to admit that finding multiple different ores in each zone somehow felt more natural to me.
Now, skinning has sort of gone the opposite way. It was always the easiest gathering profession to level, because you didn't have to seek out any gathering nodes, you just clicked to loot the body of each beast or whatever else Blizzard considered skinnable a second time to get some leather as well. Unsurprisingly, the spoils from this weren't worth a whole lot. I remember always vendoring light hides for example, because there was just such a huge oversupply that there was no point in trying to auction them for even the smallest profit.
It's still just as easy to level skinning, but there just doesn't seem as much to skin as there used to be. The mobs in most low-level areas have been thinned out considerably so you're less likely to have to kill anything that just happens to be in your way, and it's harder to find a good leather grinding spot when everything's so far apart. In addition the number of "kill ten wolves" type of quests has been reduced greatly because people always complained that they are boring, so you generally don't have reason to kill as many skinnable mobs anymore as you level up. This shows itself on the auction house as well, and I was shocked when I saw one of the aforementioned light hides go for more than a piece of iron ore. The mind boggles.
It also stinks big time if you're a leatherworker. Mind you, the skinning/leatherworking combo has involved a certain amount of leather grinding for as long as I can remember, but Cataclysm has taken it to new and ridiculous levels. My baby hunter found herself grinding mobs in Elwynn Forest for ruined leather scraps of all things, because they are the best way of getting through the first couple of leatherworking levels. I remember once upon a time I was annoyed when mobs in the Barrens still gave me scraps long after I had moved on from that, but now I struggled to get any at all! Oh, and ten levels later I was back to grind yet again, for light leather this time as my levelling had taken me onwards to medium and heavy leather dropping creatures way too quickly. What a nightmare.
Herbalism has probably changed the least, though herb spawns appear to be even more plentiful these days than they used to be. Good times to level inscription I guess, though not so much as an alchemist, because the difference between common and rare herbs seems to be just as pronounced as ever, if not more so. Case in point, I needed a lot of goldthorn to make it past a certain skill level range of my alchemy, but all I could find in the level-appropriate zones were piles and piles of blindweed, fadeleaf, khadgar's whisker and kingsblood. Eventually I looked it up on Wowhead and they actually had comments there guiding you towards what's only a handful of very limited goldthorn spawn points in multiple zones. I understand that different herbs grow in different environments and that this puts limits on how much you'll find of each - and in fact I like it, it feels more natural, unlike the single-ore zones mentioned above. For example kingsblood always grows out in the open, and since there is a lot of open space it's easy to have a lot of spawn points for it. Goldthorn on the other hand only grows on hills and rocks, which is obviously limiting - but even in Arathi, a zone which is nothing but hills and rocks, there was hardly any to be found, which I found rather disappointing. It would be nice if Blizzard considered rebalancing things like that, but I'm not holding my breath.