Limitware: get all features for a limited time or limited number of uses (ex. Textmate free for 28 days, 2GB free on Dropbox)
Freemium: get some features free forever, and upgrade to get more features (ex. Evernote, Hulu Plus)
There are even services like Basecamp which are both limitware and freemium (one project free, limited features).
I'm sure the answer is "it depends", but I'd like to here what has worked best for you guys.
I'd love to click 'Listen later' and build an audio queue that I could stream to my mobile (which is key).
The closest thing I could find was huffduffer.com, but that is not what I'm looking for. Do I just have to build the thing?
This campaign "reach" number is mostly a vanity metric, but could be useful for justifying costs to brands.