Now we can change our Virtual Worlds like we change our pants....

... no, not "one leg at a time".

IBM and Linden Labs (of Second Life fame) have succeeded in teleporting avatars from Second Life to a sim on an OpenSim server. (OpenSim is a project adapting the parts of Second Life technology that Linden Labs has released to Open Source.)

ibm-linden-lab-interoperability-announcement

While very cool from a technological point of view, I see this as a significant first step that is useful in the long run only if the avatar and all associated characteristics (clothing, animations, huds, inventory items, as well as ownership & permissions attached to existing items in each world, etc.) are also available for viewing, if not transferred for actual use. As presented in the video, and given LL's commitment to preserving creator's rights in SL, LL will be cautious about allowing indiscriminate transfer of items between environments. If inventory items are transferred, I'd expect there to be limitations governed by permissions settings (copy, modify, transfer).

As presented in the video, the process seems to work only between SL technology environments. The grid-to-grid nature of this implies an expansion of the "SLURL" addressing system, to incorporate not only the SL domain, but others as well.

I've seen references to discussions about interoperability standards between various VW's (from Linden and others). I'd expect that something along those lines would be necessary before true "web-like" access via non-proprietary systems could evolve.