I think these folks are shooting a little high for my taste. I have a different opinion on a few points:
For one, the feeling can get a little weirder if you push the dose high. Higher doses make my head feel a little flinchy and almost claustrophobic. And 10mg was enough to make me itchy. This is a common opiate side effect. It feels like your nose hairs are tickling the inside of your nose, and the itching sensation is relentless. I would suggest starting with 5 - 7.5mg for a pleasant buzz that won't have any annoying side effects. At this level, you will be able to go about your normal business, but you will sail through tasks that are usually a drag. (This functionality is also what is so insidious about opiates, You don't realize you are getting sucked in until it is too late and you have to deal with some withdrawal to get back to normal). Low doses are almost stimulant-like, while higher doses are definitely sedating. 20mg would be enough to make me feel like shit.
As people have stated, swallowing and snorting don't make a whole lot of difference with OC, because the oral bioavailability is high. If you have immediate-release ones, I still like snorting them. There is no burn, the drip isn't bad, and it comes on a little bit faster.
Another thing: While some people find their first opiate experience to be the best, I initially found the buzz to be kind of neutral, and as I did it more frequently, it grew on me (it was very readily and cheaply available). It's like your brain acquires a taste for it, and it becomes more decidedly euphoric. I WOULD NOT RECOMMEND WORKING TOWARDS THIS! This is insidious shit, because it does not feel like a big deal while you are doing it - only when you stop doing it!
These are particularly swell if you are in pain, or if you are really exhausted and want a pick-me-up without using something overtly stimulating. They can be useful for guys for sex too, because they make it easier to postpone orgasm.
As others on here have warned, these are insidious. Treat as such: Find the smallest dose that gets you where you want to be, spread your use out, and you'll get the benefits without the horrible pitfalls.