The company I work for has just invested in Hubspot to market our own company to begin with. I will let you know how we get on with it. I originally took the call from a guy trying to sell it to us as I requested a free trial. I ended up telling him that it wasn't right for our business as creating automated landing pages for ourselves and our clients would actually take work away from us. We mainly build websites and landing pages you see. I felt like he was effectively trying to take our clients onto their platform and we would see a few crumbs of commission. I also said we have access to all the data they provided using multiple online software. So I declined.
Our owner/manager has recently bought into it thinking that inbound marketing is the future or marketing and I would have to agree, it is why I signed up for the trial in the first place (Once all of the technical aspects of SEO have been taken care of, it then becomes more of a marketing role). However, I did think it was something that we could manage ourselves as David has said "use 3-4 third party applications instead". This can be quite time consuming when your client list starts to stack up.
I am still skeptical as it still requires a lot of hard work and money. It's not like they create any of the content for you. I will let you know the progress we have made with it in a couple of months. If you don't hear anything from me.....I doubt it will have been very successful 
PS. I hope this all makes sense I typed it very quickly