I got my first siege ever today - 16 pikegoblins showed up and started meandering towards my fortress. I have to admit I wasn't very impressed, since I've faced more than 16 goblins from mass ambushes, and those had ranged attacks; I could've just raised the bridge, stationed some soldiers at my overlook tower, and killed them all quite easily. But I let them come anyway, just to make it interesting.
When they were about halfway to my fort, a hydra showed up. On the other side of the map. Bugger moves quickly, too; he rapidly found my secret entrance (which, really, wasn't all that secret; it's mainly a shortcut to new tree growth) and mowed through my poor guard dog, ignoring the spiked iron ball traps I'd set up (granted, each trap had only one ball, as I wasn't certain when I made them how much iron I had available). Then he met the trap I'd set up because I really, really didn't want to devote the time to guard that entrance 24/7. It had four warhammers and four axes in it, all iron, a product of my lessons in weaponsmithing after I'd learned just how extensive magnetite clusters were.
Let's just say I never really got to find out how burly hydrae are in combat. Though I'm sure there will be other opportunities. Surprisingly enough, the hydra corpse is all in one piece, too. At the very least I'll get some hydrabone bolts to play with, and one hydra skull totem.
As for the goblins, I just massed my 27 military dwarves (some hastily equipped with crossbows, 'cause hey, even untrained crossbowdwarves are better than moderately-trained wrestlers) and set 'em loose on the horde. 9 died, 7 fled, and the only damage I sustained was a temporary setback in my ammo supply (temporary, 'cause all their iron gear will be melted down into new sets of iron bolts). Not a single goblin triggered a trap.
So, yeah, when do I start getting sieges with 30 or 40 goblins? *waggles eyebrows*
Edit: I should note that over 1/4th of my population is military, because I can't find sustainable jobs for more than 40-50 dwarves.
[ March 24, 2008: Message edited by: Derakon ]