I never found that to be an issue getting friends to sign up for Venmo. You don't need to enter any info to accept cash. It was getting them to realize this was cash and not some magic points (because they dont know what venmo is). Snapchat should kill it here because people already understand and trust (for the most part) Snapchat and this is just a new feature - not an entirely new service to learn.
Recently I have been taking the approach of "I sent you $15 for XYZ on Venmo if you want it you need to signup" because it's one of the few ways I can get them to do it. I hate to hold their money hostage like that but if I don't there isn't a great way for me to give them money other than paying for them up to what I owe them the next time we hang out (which I am bound to forget).
I agree, I feel like Snapchat/cash will kill in this space due to ease of use.
