I used to be an avid user, but I quit a few years ago. I didn't have any negative side effects for years. Eventually, though, I started noticing some cognitive impairment after use. If it's just the next day, it's no big deal. I could use ghb on a saturday, feel a little stupid on sunday, and be back to normal for work on monday. I don't know what changed, but the "feeling stupid" phase seemed to last longer after each use. I got to the point where I could take one dose on a friday night and still feel impaired on monday and tuesday. It wasn't worth it, so I took a break for a year. I tried it again once, had the same problem, and decided to quit for good.
I don't know how common that side effect is, but I didn't have that problem at all until I had been using it for years. It wasn't anything permanent; I got back to my normal self when I quit. I'm guessing a lot of people never have that side effect in the first place.
I never had a problem with addiction, but I don't have an addictive personality. If you think you do, just be careful. A friend of mine is like that, where he can't have any drugs in the house without using them. I'd give him a bottle of ghb that would last me 6 months, and he'd use it all in a week. All you need is a little self control. I'd set rules for myself, like no drugs when I have to work the next day. I'd stick to those rules, so addiction never came up. It's a little riskier if you start using it every day.
I had fun while it lasted, though. It doesn't seem like a "hard drug" to me like opiates or cocaine. It's not going to bring you a life changing experience like LSD or MDMA. For me it was like a better version of alcohol with a few extra benefits (like the enhanced sex). If you like the effects of alcohol, just do the same fun things and use ghb as a substitute. Play video games, watch movies, go to concerts, etc. I used to put a dose in something like mountain dew and chug the bottle right before a concert (if someone else is driving). Just don't mix it with alcohol. It can be mostly safe on its own, but drinking alcohol with it makes it much more dangerous without it being any more fun.