I have been using evernote for several years, mainly as my digital storage of reference information, beeing a scientist I have a large archive of pdf files stored in evernote.

regardless of which program or system you use for GTD there will always be a large number of tasks that need to be done on a certain date or time and you need a physical reminder (a beeb, an email, or popup) to remind you of it.

So far evernote does not include any calendar function to do this, untill it gets that evernote will be a great for storage (probably the best), but useless as the only GTD tool.