Arc10 and future releases will not include the Single Output Map Algebra tool. But not to worry, Arc10 and future releases will run in existing models and scripts which contain the Single Output Map Algebra tool. We have deprecated the Single Output Map Algebra tool starting in ArcGIS10. To replace this tool we have created a new Raster Calculator tool which will be available as a patch on top of prerelease
There is a forum post about this but the short explanation is that we changed map algebra syntax in 10 to make it work better with python. We can�??t have two very similar languages so the old syntax is no longer used in 10, therefore SOMA, MOMA, and the calculator from the spatial analyst pulldown menu are all gone. To replace them all is a new Raster Calculator tool that is nicer than the old map calculator, AND can be used in a Modelbuilder, scripts and will support the use of variables.