I was a little bit of a late arrival on the scene of the Arisia/Boskone split. Despite knowing as a child that SF conventions existed, and despite the presence of one (LosCon, which was similar in many ways to the Boskones of yore) within easy bicycle distance to where I grew up, I never attended an SF con until after I came to Boston for college in 1988. Even then, I missed the Worldcon in '89, and my first convention was the first Arisia in 1990 (which I ghosted). I thought it was tremendous fun and started going to the other large East Coast conventions right away -- at the time, that was Arisia, Lunacon, Balticon, Disclave, and Philcon. Boskone was still in Springfield, which was difficult to get to, and although I had a vague understanding of it as being boring and unwelcoming of younger fen, I think it was really the location that kept me from attending.
My first solid perception of NESFA was formed in the spring of 1992 when I was invited to represent the Harvard-Radcliffe Science Fiction Association at an MCFI meeting whose purpose was to explore the possibility of a bid for another Worldcon in Boston. This meeting was run by Priscilla Olson; she organized activities for the participants which I thought ranged from boring to patronizing and gave me the impression that she was uninterested in anything that I might have to say. Priscilla, like most MCFI members, was and is heavily involved with Boskone, and I and many others consider the two organizations to be different aspects of the underlying social group which comprises their respective memberships. I have since forgiven NESFA, but I still hold a grudge against Priscilla for the way she ran this meeting.
Meanwhile, I was getting more seriously involved with putting on conventions, joing the Philcon committee in 1991 and the Arisia committee shortly afterwards. Within a couple of years I had decided that I wanted to chair an Arisia, and started to pay attention to their organizational politics (which at the time were treacherous). I pretty quickly figured out that the fact that I had never been to a Boskone was a political advantage, particularly with recruiting from UMSFS-B and other student organizations, and with convincing gafiated Arisia founders to work on the convention. I also recruited from Readercon and to a small extent from NESFA, and while that might have been made harder by my lack of connection to those groups, I don't really think many of those people would have been willing to work for a 25-year-old who'd only been going to conventions for a couple of years, even if the conventions in question had been Boskones.
After being passed over for Arisia '95 Chair, I joined the board of the Boston Convention Engineering Corporation, a splinter group formed from MCFI over a disagreement about how to bid for a Boston Worldcon. For the next two years, these two groups effectively bid against each other for a Boston Worldcon, with BCEC playing on the Arisia/Boskone split to recruit heavily from Arisia, forming a strong parallel in a Worldcon bid rivalry to the rivalry between the regional conventions. Intra-city bid rivalries are not unheard of in Worldcon bidding, but this was the first time one was taken as far as the actual vote, which I think raised the profile of the local rivalry almost as much as the 2004 ALCS raised the profile of the Red Sox / Yankees rivalry.
After chairing Arisia '96, I took a year off, during which much of the aforementioned treacherous politics came to a head and there was a small explosion of the Arisia staff. Three or four of our more dedicated staff, people who were considered likely future Con Chair candidates, defected (and that's really the word) to Boskone during this time, and a couple more disappeared and haven't really been heard from since. Although the issue that caused the blowup was internal to Arisia, it really was the watershed event that allowed, on the Arisia side anyway, for a reconciliation between the two groups. I think the defectors still hold a grudge against Arisia as an organization, but meanwhile they have been working to reintroduce some more youth-oriented aspects to Boskone, and the generally lower political angst level has probably contributed to our ability to recruit from NESFA (and vice versa). The increasing connectedness of the groups was acknowledged formally when we asked longtime NESFAn Sharon Sbarsky to be the Arisia '00 Fan GoH, and again when we asked former Noreascon chair Tony Lewis to be the Fan GoH for Arisia '03 (though when he got the invitation, he had the police test it for Anthrax before he would open it). Likewise, Noreascon IV asked BCEC chair Don Eastlake to run the WSFS Business Meeting, which he considered a great honor.
I still think Boskones are boring, but I do go to them now. And MCFI is still much more closely associated with NESFA than with Arisia, which has meant that Arisia's staff didn't get burned out as much as Boskone's did by the effort of putting on N4. BCEC is pretty moribund right now. MCFI has added a few new members, but they and Boskone are both facing problems with replacing staff as they die or grow too infirm to work on conventions. I don't think MCFI as it is currently constituted can run another Worldcon in Boston. But I think this is all due to a more important difference between Boskone and Arisia, one which was present at least as early as that meeting in 1992 and is certainly prominent now. The Boskone committee is a social group at least as much as it is a convention-running organization. NESFA members get together weekly at their clubhouse and even business meetings have a social aspect. Although recruitment for Arisia often happens through social connections and there is a strong overlap with the Elbows/Suspects community, Arisia is not itself a social group, does not have a clubhouse, and values brevity over community in meetings. I think this has been a hindrance to NESFA's incorporating younger members, and although a tightly knit social group is an advantage when trying to put on a crisply run convention without an enormous committee, ultimately I think it's why MCFI will die with its current membership.