This should be shared as widely as possible.
There's a change coming to OpenSim that will require everyone to upgrade. This is my understanding of it, from talking to Melanie (any factual errors are mine, and will be corrected once spotted):
There's a bug, in the current release (and earlier) that limits OpenSim's ability to support additional wearable types, such as those recently added by LL. This bug will be fixed in 0.8.2 (and in a version of 0.8.1 Post Fixes, that will be released at the same time as 0.8.2). No 0.7.* version, or earlier, will be fixed.
However, TPing from the fixed code, to older code, would cause the region running the older code to crash. So, TPs to older code will be denied, via a change to the protocol version.
For my grid, Sanctuary, this means that when I update, virtually all of my gates will no longer work - at least until the destination for a gate updates to 0.8.1 Post Fixes or 0.8.2. If you come to Sanctuary to visit The Spirit of Arcadia museum or the Ivory City, you will be able to get here, but you will not be able to TP away, unless you go to an updated destination. Instead, you'll have to log out and log back in elsewhere.
I assume that this means updated regions will not allow TPs to regions running MOSES, ArribaSim, or any other non-Core OpenSim code, unless the folks who maintain them make changes to remain compatible (i.e., fix the bug and bump up the protocol version).