[nl]

Eric Ries has written extensively on how he initially spent months engineering cross-IM compatibility for IMVU, and then when they shipped it he found that a large number of their customers saw separate IM networks as a strength, not a weakness.

They'd say, "Hey, that guy was neat; I want to add him to my buddy list. Where's my buddy list?" And we'd say, "Oh, no, you don't want a new buddy list; you want to use your regular AOL buddy list." You could see their eyes go wide, and they'd say, "Are you kidding me? A stranger on my buddy list?" To which we'd respond, "Yes; otherwise you'd have to download a whole new IM program with a new buddy list." And they'd say, "Do you have any idea how many IM programs I already run?"

"No," we'd say. "One or two, maybe?" That's how many each of us used. To which the teenager would say, "Duh! I run eight." It started to dawn on us that our concept was flawed.

Our early adopters didn't think that having to learn a new IM program was a barrier.

http://www.inc.com/magazine/201110/eric-ries-usability-testi...

[matt_kantor]

I already mentioned this in another comment, but it's also relevant here: I don't understand why it's assumed that contact and identity isolation should lie at the service provider boundary.

People are able to manage multiple email addresses and phone numbers for work/personal/whatever without too many problems, and despite being against Facebook's terms of service many individuals already create more than one Facebook account to keep stuff separate ("I don't want my boss to see photos from that party last weekend"). In a standardized IM interop utopia I'd imagine that juggling multiple identities would be even more common.