Hi Michael,
Please in the future post questions about working with source code in the devleoper forum not the Installation forum.
Speeding up the build is in the grand scheme of things much less important to me than other things such as having a working solution that allows you to keep custom project code spearate from core code.
There is no confusion about which data layer is used, The Data layer project used is always the one referenced by the Business layer project. The download .zip of source code and the svn trunk version are always referencing MS SQL unless you change the reference. If you are only using MS SQL you can copy the mojoportal.sln file and rename it then use your custom.sln file and remove the data layer projects for the data platforms you are not using, ie all of the Firebird, MySql, pgsql, SQLite projects can be removed from your solution. When I produce packages for other dbs I change those references on the business projects before building and the appropritate data dlls land in the Web/bin. The data layers are designed to have the same name across db platforms to make sure there can only be one data layer dll at a time in the Web/bin folder. In fact they all have the same namespaces and api and data layers are changed merely by changing which dlls are in the bin. I'm not going to change to dll references instead of project references because things are constantly added to the data layer projects.
You can also remove the SiteOffice projects from your solution if not using them and probably you aren't since it is just prototype stuff at this point.
Hope it helps,
Joe