I like how easy it is to add new pages or modules without having to worry about compatibility issues when upgrading from one version of Sharepoint to another. The layout isn't always what you'd expect - sometimes there's too much going on at once which makes navigation difficult! It also doesn't have many features out-of-the box but can be customised easily. We're using Attollo as our internal portal so we've been able to quickly build an area where members are encouraged to upload their work in progress documents.