In the ArcGIS 10 depreciation document this little tidbit catches my eye.

ArcGIS Server 10.1 will no longer support 32-bit operating systems. ArcGIS 10.1 will exclusively support 64-bit operating systems. Support for 64-bit native execution across all the tiers of ArcGIS Server has been a long awaited feature by many of our customers. 64-bit hardware is the norm in today?s market and most modern ArcGIS Server deployments do in fact run on 64- bit hardware. ArcGIS Server 10.1 will run as a native 64-bit application exclusively requiring 64- bit capable hardware.

Now we are talking about Server here, not Desktop, but a total 64-bit server suite is very nice. One more thing that for some reason seems to get people a bit riled up:

ArcGIS Server 10.1 will no longer support publishing non-optimized map documents (MXD files). ArcGIS 10.1 will only support publishing optimized maps (MSDs) as that is the best practice for map publishing. At ArcGIS Server 10.1, optimized map services (MSDs) will be enhanced to support many of the capabilities that are currently only available through MXD-based map services.

This is a total performance change now that MSDs will support just about everything you need from a cartographic standpoint. Oh and one last little tip of the hat to the workhorse:

There are no plans to release a new version of ArcInfo Workstation at ArcGIS 10.1.

Frozen in time will ArcInfo Workstation be (hmm did I just channel Yoda there?).