For me, I've made a few acquaintances over the years, but I've made lifelong friends online. Friends that would mail me stuff for free or for the cost of shipping, and vice versa, friends that wrote me while incarcerated, friends that would talk to me on the phone when my real life friends weren't around back then. 2 of my friends at the very least, I've consistently communicated with them since like 2005. So for me anyway, a few of my "internet friends" are more reliable than my real life friends, I can think of no real life friend that's consistently been my friend since 7-8th grade. Keep in mind, without internet even, these friends would talk to me on the phone like over 5 times a week easy for like an hour at a time.
Besides these super reliable friends, from my old pool of "friends" on AIM, there's about 5 out of the 20 or so I used to have that I still talk to regularly, but I believe that's more from not being online for about 2 years.
I think my big problem with online friends, they just randomly inexplicably disappear, sometimes it's legitimate, but most of the time, I find out they blocked me or something. They're usually not ballsy enough to just tell me what I'm doing wrong, and actually seem to act very friendly or whatever toward me, and just block me later. So that sorta passive aggressiveness is something I dislike in online friendships. It happens in real life, too, but in real life, most of your friends are in a close proximity to you, so you know sorta what's happening, or you can resolve the situation easier, etc. Online, though, it's much easier for people to press the block button and not say what's wrong.
An alienating thing, too, my refusal to participate in new social networking sites and stuff. I'm stuck in my old ways, using AIM, etc, and not being cool and using Skype and Facebook and stuff. So that makes things worse with my real life friends, who've discovered the magical internet.