Overnight I tried to think about where the dissonance in this thread is coming from. It's not from John certainly, nor from Square's business model per se. But I do think there has been a long-simmering, and still growing, discontentment regarding the valuations of many newer tech companies, and how disconnected they appear from fundamentals. This was all brought to a head with the IPOs of ZNG, FB, and GRPN, which have lost public market investors $80 billion among them. That the pre-IPO inflation was so deliberate and intentionally stimulated by early investors and management lends an inherent skepticism now whenever any company closely affiliated with that world does something that seems far out of line with rational expectations (e.g. leases massive amounts of some of the world's most expensive real estate to house 6x employee growth in a year). So the Dropboxes, AirBnbs, Squares, Spotifies, etc., are all painted with the same brush, whether or not they deserve it. (And again, Square as a business quite possibly is different, and they certainly have hired world-class talent.)
Mostly, people are just afraid of a bubble. Or rather, what happens if and when the bubble pops.