-- For SMBs looking to create Internet or intranet sites using the standard features of SharePoint Server 2010. For companies who want to host the server on premises.

-- Similar to Standard Edition, presumably with more scalability and management functions. An exact list of how this differs from the standard edition is hard to come by. (Ditto for a features list on how Internet Sites standard edition differs SharePoint Server 2010).

-- the FAST search engine is added on top of SharePoint Server 2010 for Internet Sites, Enterprise. If you don't want to spring for the high end FAST search server, Microsoft will be releasing options for the enterprise to use and I would assume that by opting for these less scalable and less sophisticated search servers you will reduce the cost of new SharePoint 2010 server licenses.

-- one of two cloud versions of SharePoint. Note that hosted SharePoint is already available from Microsoft via its (BPOS), which combines hosted SharePoint with hosted Exchange. Microsoft counts more than 1 million users among those using some version of hosted SharePoint.

-- It isn't clear how this will differ from SharePoint Online, except a good guess is that it will support more online capacity. One of these cloud versions will be under the software-plus-services model, for companies that want some SharePoint sites to be hosted on premises, with some sites available via the cloud. The other will be a fully hosted option. Microsoft says that these options will be half the price as on-premises SharePoint because Microsoft will not require CAL licenses.