The first time I did heroin was a spur of the moment decision I made ten minutes before I had to go to work. I insufflated a little over half the bag and took the short work from my house to my place of employement. Went into the bathroom and finished the rest, then went to punch in.
By the time I got to the front end and started my 'work' (bagging groceries) everything started to seem a whole lot brighter. A feeling of warmth came over me, my eyes were looking straight ahead though I wasn't quite sure what I was looking at. The euphoria wasn't as intense as I would have expected, feeling like the buzz from a high dose of hydrocodone. Opiates mean itchyness and damn did it feel good to scratch yourself. It wasn't until the high was fading that I became nauseous and vomitted, only liquid came up and it was as if I didn't puke at all.
Since then I have done it about five more times, each time the dose was a single bag. Some day i'll do two, some day. A warning if you plan on trying this drug, it makes your pupils very, very small and they stay that way for quite some time. Up to ten hours as I remember.

My experience with 'speed' or amphetamines is more limited. I tried it in the form of Adderall which is a mix of dextro and levo amphetamine, as opposed to just the more potent and probably more enjoyable dextro isomer (Dexedrine). Also insufflated, I remember feeling wired and restless followed by chills, fatigue and inability to sleep. I see its potential as a study-aid, but recreationally it fell short of my expectations. Maybe if I get some Dex i'll give it a retrial.