As an agency, we use Act-On to manage all our clients' marketing automation efforts. And that covers a lot of ground: web and social tracking, form submissions, content downloads, list management, lead scoring, landing pages reporting and, of course, email programs. The Act-On ecosystem is solid and each of the pieces complements each other well enough to create a marketing automation whole if that makes sense. So your emails "know" who visited what landing page and your forms "know" if this person has downloaded other content. This connected system allows you to build complex marketing campaigns, all within the Act-On system.
That said, we use for all of the above. Mileage varies from client to client, but we certainly use every part of Act-On. We will build our client landing pages in Act-On, we house our email templates in Act-On, we upload marketing content to Act-On -- I'm in it all the time! In fact, I have it open in one of my browser tabs as I am writing this review.
Overall, it is a solid marketing automation platform. Act-On manages lists, segments, email programs, and sync's with SalesForce very well, but in some areas like landing page design and reporting it falls short.