I'm curious how deeply you went for an integrated approach for projects / email / tasks / files. I find the more integration you do, the more learning users must do vs. individual applications with loose integration that are more familiar to users (that behave like those in the title).
I've spent a fair amount of time trying out both personal and business team workflow in Trello, Jira/Agile, Asana, Google Apps, Evernote, etc.
Currently giving a couple weeks of my productivity to IQTELL (http://iqtell.com), which goes for a heavily integrated full-on GTD approach that I'm finding rather refreshing (everything in one tool!). Was waiting for the past few years for them to figure things out and open to the public. It has its own issues and learning curve, and lacks that final 20% polish that makes Trello and Asana such a pleasure to use. But with such deep integration between email, projects, tasks, contexts, contacts, calendars, and Evernote (would love direct Dropbox file access), along with a fair amount of customizability, I'm finding the learning curve to be worth it.