CritterNYC hit the nail on the head.
AOL closing down their USENET connection is indeed a major milestone.
I remember before AOL was on the net... back when there was no spam on USENET, when discussions were intelligent.. you know, when we had to walk uphill in the snow both ways to school.
I believe that the AOLization of the internet is a major event in the 'nets lifetime. AOL connecting to USENET was a major part of that. I remember when AOL users began to show up on IRC. People didn't like this at all. Their arguments back then for why AOL users shouldn't be allowed on the internet went like this:
AOL is like CB Radio in its heyday-- anyone can use it and it takes virtually no skill to operate it. There are only 40 channels and most are full of people experimenting and learning to communicate using the radio. There are some "pros" on there, but they are far and few between.
Now some people liked CB radio so much (or were so frustrated by the fact that it was clogged up by abusers, as is the case now) that they wanted more. They turned to Amateur Radio, which had been around longer then CB radio and requires people to take a test to become licensed by the FCC in order to operate.
Before AOL, the internet was like Amateur Radio-- anyone can use it but you have to learn a thing or two before you can operate it. There is an almost unlimited spectrum of frequencies and modes that you could choose from and there are communities all over the world to help you along your way as you use it. But there was that test, that you had to learn a thing or two to even use it in the first place, that filtered out people who didn't care enough to "pass it." That test imbued a sense of community and respect into the users for the system and that is why, to this day, CB radio is virtually unusable for citizens (as opposed to truckers, atleast in the states) whereas Amateur Radio has prospered. These days Amateur Radio operators build and launch special amateur radio satellites into orbit-- the international space station has amateur radio experiments on it. There are even plans for Amateur Radio equipment to be sent to orbit Mars. Amateur Radio has even provided and continues to provide emergency communications during things like 9/11 and the recent tsunamis, and these are just a few things that Amateur Radio has accomplished or contributed.
Now, when AOL turned on their "internet gateway" they unleashed the world of CB into amateur radio. Suddenly millions of people who would otherwise be in a sandbox to experiment in are now flinging sand all over the place and getting everyone dirty. If CB had been combined with Amateur Radio in this manner the world would never have seen Amateur Radio satellites (there are 15 in orbit that are currently operational)--and can you imagine CB being used on the International Space Station?! Would Amateur Radio continue to be viable for use in providing emergency communications?
USENET and IRC users knew AOL users would create a problem, and they were right. However what wasn't foreseen was that some people began taking advantage of these AOL users en masse- AOL users for the most part didn't know what they were doing on the open net so they were perfect targets for junk mail, popups, misleading ads and adware. AOL users were so fresh to the 'net that they didn't grasp the concept that they could get junk mail in the EMAIL box just like they could with their POSTAL box and AOL users didn't know to differentiate between pop-up ads and web pages, just as they would differentiate between infomercials and television shows. After all, "You've got mail!" was an announcement they looked forward to, not expecting to get it every time they signed in because their inboxes were always full of spam. AOL users clicked the links, bought the products and launched the spam industry.
Though the number of people susceptible to spam and adware is finally shrinking, the facts are that spam and such is made for the type of users AOL brought to the internet. We've all been made to suffer because of this. AOL killed the internet as we knew it. We shouldn't blame AOL specifically though because it could easily have been Prodigy or another "online service" that ended up dumping millions of people into the internet ocean without life preservers or shark repellant. I just wish that AOL had taken more pains to separate their "sandbox" from the rest of the playground-- perhaps moderating their users as they connected to the 'net and eventually granting them a "full internet pass" or something of that sort.
The bottom line though, is that we all had to earn *our* "passes" through things like VT100 terminals, PPP and SLIP. Would the internet be a different place today if AOL had made sure their users earned their "passes" too?