I did it a lot in my teens into mid/late 20's. There was a period where I was doing it 2-4 times a week, sometimes by myself and sometimes in large quantities.
Never really had a bad trip myself, had some pretty intense ones though, like seeing Natural Born Killers at the Mall of America and then sneaking into Camp Snoopy, or taking a 10 strip at an outdoor Metallica concert and losing my contacts. Playing games was really fun, the Sega CD was out at the time and the FMV games were mind-blowing, also The Terminator was really cool because it had surround sound.
Though I certainly witnessed a few, mostly from people who had little or no experience taking too much. I just got bored/burnt out on it, also the opportunities for taking 8-12 hours for a trip dwindled down, but I did do it on a few special occasions later, like going to Vegas.
The things I didn't like about it is that it can be very "speedy" depending how it's made, so you'll be grinding your teeth and it'll be hard to get to sleep afterwards. If you smoke, you'll do so like a fiend. The comedown/next day can be a hassle as well, as you brain sorts itself out.
If you're a first timer, I'd say to start out light with a half-hit and be around a small group of friends, in a chill place or in nature, preferably with at least one other person who has done it before. You're generally not want to be around drunks or other loud people, clubs/bars, etc. until you have more experience. Good weed will help with the comedown. Do not drink or do anything else though until you're more used to it.
