Ben Evans takes a look back at Facebook’s acquisition of Instagram. From a pure number of users standpoint, it’s looking like an extreme bargain. Instagram was growing fast, but it’s growth has exploded post-acquisition. On the other hand, there doesn’t seem to be any clear winner for mobile sharing – photos or otherwise. As Ben has often pointed out, mobile habits seem extremely fragmented with people using multiple services, each with their own cross-cutting and overlapping use cases.