Hi,
You are correct about installing it on all nodes and point to the same db, but the below issues still have to be addressed.
Currently mojoPortal doesn't support web farms because many files such as images, cache dependency files, and also the search index live in the file system, not in the db. So if a user edits content and uploads a new image it will just land on one node and the file will be missing on other nodes unless you have some mechanism to keep the file system in sync. I plan to implement an add on product for Web Farm support hopefully by this fall.
Until then, you can still use it on a cluster if you can come up with a process to sync files accross the nodes. You would also have to just do without the search feature for now in a web farm because I can't think of a good syncing strategy for those files as all nodes would write to them potentially at the same time. You could remove the search link from the skin.
Or if all the nodes share a common file system it can work with no problems and in this case the files would be installed just once in the common file system.
Hope it helps,
Joe