Critters will continue to follow you if herded, until they're tamed, die or you herd them in a different direction
They will also stop following if they're peaced (bard), confusion blasted (potion), damaged by aura or area spells, or they aggro or are aggro'd by another person or creature.
To the OP: the 3 basic moves are:
Pin: Herding a creature onto itself will keep it stationary, just mash your last object(crook)/last target(creature) macro. Handy for taming creatures that "anger" such as dragons or cu sidhes, works best if you have a tamer & shepherd working in tandem.
Pull: Herding a creature onto yourself will make it follow indefinitely unless one of the above conditions are met. If you teleport to any part of the same subserver, the animals will bee-line to you if possible. Leave a subserver (eg: exit a dungeon) and the creature will head west. There is no theoretical limit to how many creatures you can pull at once. I have herded all of Dagger Isle's arctic creatures at once, was a tad laggy though.
Push: Herd a creature to anywhere else and it will walk to that spot at NPC-speed. One trick is to "push" it to a spot, then as soon as it begins moving, "pull" it to yourself and it will complete the push destination before returning to you. I've sat at the bank "boomeranging" critters this way and it baffles some people. You can also try pushing, pulling, then pinning before it returns to you to fudge a faster push. Good for positioning your own fighting pet between you and the spawn, or for clumping targets together for barding.
What you can herd: All tameables, and champion spawn "tameables" (even though champ versions
aren't tameable). Slimes, rats, wolves, imps, kirin, unicorns, drakes, dragons, etc. The only tameable that can't be herded is the fire steed, even when discorded. I believe that to be a bug as other top-end tameables such as dragons and cu sidhes can be herded at around 60-65 Herding. Herding's extremely easy to gain now since the last skill-gain changes, you don't need fresh targets. Just get yourself some pets (scorpion, gaman, hiryu) and mash away, or go looking for creatures about 10-20 Taming requirement below your Herding skill.
Herding's very useful in that most of PvM and some aspects of PvP are about spawn management. Being able to bring the "mountain to Mohammed" is a powerful thing.