The allocation of IO resources to volume initialization is something that really needs addressed.
Apparently, the latest release candidate takes care of this on the ftp server (it's in beta, now). I haven't tried this out, but this should soon make its way to a full release, available via software update (online update).

Active-active replication is possible, but would require something like a SAN filesystem anyway, so it wouldn't be that useful (active-active replication is available in drbd, which open-e uses) for the most part.

Another nice feature which just came out in drbd is the ability to do replication via low-latency infiniband (not just infiniband-over-ip), using the sockets direct protocol. This is really neat, and is something that other SAN providers are working on for next-gen very high performance systems. We don't have any customers that need something like this, but it would be a good way to all but completely mitigate the performance hit from replication.