A somewhat off-topic word about dosing:
250 μg used to be the standard dose of acid in the original heyday of the hippie days especially in microdots and such. Dose per "hit" tapered off afterwards. It's inaccurate to say that WLP dosed "his" acid to so-and-so many micrograms, though, becauae he wasn't involved at that level of the business: he sold it in much bigger bulk and crystal form (very cheaply, from what I've heard it was easily more than an order of magnitude cheaper than the price per "hit" to the end user, I was never involved firsthand with that though in that era), other people laid it onto blotter for whatever other retail form. He may have laid the occasional blotter but wasn't doing the laying of the commercial stuff that was made from his product. By those days I think a dose of 100 μg per blotter (i.e. 10 tenpacks or 100 sheets to the gram) was already pretty standard, some stuff being a bit weaker by people trying to squeeze a buck.
This standard persisted throughout the time I was involved with that stuff. Higher-dosed blotters (&etc.) are novelties and honestly I don't agree with people laying stuff stronger than standard because it can get people into trouble. There's simply no reason for it. I'd much rather people sell standard-dosed blotters cheaper than sell higher-dosed blotters at a stupid price per hit/sheet which seems to be the route gone by the internet drug dealers.
As to the dose, I'd consider 250 μg to be not extreme but rather a proper solid trip, where you're completely into the experience, a +++ in Shulgin's terms, maybe +++½ at most set-and-setting dependant, but not a ++++, that takes closer to 0.7-1mg IMO. 250 μg is just a good, solid dose of acid that produces a classic well-defined trip.
However, very few people actually know what "mics" feel like and you have to be really careful listening to drug dealers about the dosing of their product. Generally speaking people tend to over-rate the amount that they take when people try to throw around numbers estimating how much their dose was when they trip. 250 μg, don't get me wrong, is plenty and a good solid strong dose. Even 100 μg is nothing to sneeze at, a light and breezy casual recreational dose, where you can go about your business like you were sober, if anything can be called that with acid, is lower.
As far as Hoffman goes, I'm also pretty sure he took more acid than that, although hardly as much as some of the acid evangelist types. He preferred lower doses than people like Leary and the Dead, too (see: microdosing and "Hoffman cocktail")