My experience – it has to clearly solve a problem where the pain is there.
We could have a debate on definition of Gov 2.0 but I think the most successful ones have that:
-Open source CMS (Drupal/wordpress) – all agencies need a CMS. Most don’t like their current one and have looked to change them. So change there
-SaaS email (often Google or Microsoft) – all agencies have email for their staff. Most don’t like their current one as the storage is low and takes a lot of resources. Plus people often have better experiences in personal email accounts. So you’ve seen a lot of adoption of Microsoft cloud email and Google apps for gov
The ones where it is simply nice to have (we should collaborate more internal for example), I think is just a harder change as no impetus to move tomorrow.