I’ve been using Evernote since 2006. The combination of checkboxes and their searchability with the “todo:” search operator allowed me to manage my GTD workflow in a particular manner. Other third-party solutions, such as Zendone, utilized notes as to-do items, ignoring built-in checkboxes altogether. But then when Evernote released a new “Reminders” feature, they piggybacked on it by making the reminders behave as to-do lists, with their own checkboxes, completely separate from the ones in notes. This was a little problematic, as it creates serious fragmentation in your workflow. Perhaps it can be used for “focus” items. I didn’t like the old checklists, but I used them. I like the new checklists, but the fact that they can’t be correlated with the existing ones makes a transition difficult, and though reminders are supported in the API, they are not supported in the free-text search syntax or saved searches, both of which I use in my regular workflow. (Another area of fragmentation is that Reminders aren’t available in the Windows version.)
Enter Springpad. The only way you can enter a checklist is as a separate note type (just like in Google Keep). I don’t have a workflow planned up yet, but I’m starting to get some ideas. I also like the “comments” feature, and though this is used in so many modern platforms (blogs, Facebook, G+, etc.), because of my background, I relate it to software development PM apps like Bugzilla or OnTime. Evernote has collaborative features, but it does not have this ability to identify who wrote what when.