I am in charge of improving our team website, developped in Sharepoint. However, due to old license (we use Sharepoint 2007), the lack of features and the lack of admin rights (wich is quite specific to our current setup), I consider more and more the option to start a Liferay portal from scratch.
I would thus know if there is any compatibility between the 2 platforms, so that I can transfer existing data (especially user data) from one platform to another.
Although your question is on a high level, I'd attempt to answer it with as much area as I can cover. Hope that helps!
I worked on the design of a project where one of the goals for me was to Migrate 'data' from SharePoint to Liferay.
Well, as the case with most migration projects that I designed/developed, there's no generic tool to migrate data to Liferay from SharePoint.
You'll have to use webservices (either Liferay consumes SharePoint services, or vice versa) to migrate your Information. FYI: Liferay provides both SOAP & JSON/Rest based web-services to choose from.
Write custom portlets to fetch data from the data-source and populate it as per your requirements in Liferay. I've chosen this approach over webservices most of the times for its simplicity and power.
You may also want to use 'Liferay Sync' for migrating your documents. You can export your documents from SharePoint on the file system and map those folders with Liferay sites/document libraries using Liferay sync.