I have seen a number of goblin sieges in df2010, they come thicker and faster than the older versions. In my experience theres always more than one squad (even in ambushes for me) and squads are of at least 5 goblins, although 10-15 is more typical. All golbins in the same squad wield the same weapon, they are rarely wresters, spears, bows, axe, hammer, sword all being common. The biggest siege ive seen had about 140invaders total. Once your getting voer 30 goblins, or on your second seige or have lots of wealth (dont know exact numbers) you get trolls as well. trolls come approx 1 to every 5 goblins. Also goblins bring mounts. This seems abit random. Ive had large sieges with just one or two mounted, and medium or large sieges with almost every goblin mounted. They often come mounted by the squad.
As far as gear and skill goes, they generally have a mix of copper and iron gear, with breast plates being less common than chainmail. I dont know about skill tbh, as i cant check it in game (is there a way to do this?) but i guess they are between average and competant skill based on their combat ability. A dwarf with iron or better chainmail, and competant skill will usually dispatch two or more goblins sustaining minor injuries. They will butcher untrained or poorly equipt soldiers easily. War dogs are almost useless, big war animals can fare better. Stone fall traps dont do much, cages are still awsome, flooding traps work best (sort of).
I dont think their strategy of waypathing has changed much since older versions. They just hunt anything alive on the surface and then charge your main gate. If you close your main gate and they cannot waypath things get odd. They will just sit around until you reopen. When you do reopen often only one or two will attack you initially, making using flooding traps a right pain in the butt as you can only get two or three at a time, and my traps tend to take an age to drain for reuse.
Goblins dont appear to flee as easily as they did in older versions (e.g. kill 4 and 40 run). If they sit round out side for along time some drift off whilst others sit there. They will flee but you have to kill most of em.
wealth appears to the biggest factor in determining siege strength, rather than years of fortage or population. I hit adamatium early in one fort, and one of my dorfs decided to make an artifact out of it. I had about 30 dorfs and huge fort wealth in the third year and was getting two sieges a year of 40+gobos.... your strength has failed
that about somes up my experience which is based on about a dozen sieges, others must have more excperience than it though, and my obeservations maynot be the norm