I'm actually a little disappointed in that 1.5M number. Mint is held up as such a success story, I had assumed, given things like Dropbox's 4M number, that Mint would be much higher.

For those of us that are in much smaller niches, and with expectations of less press coverage, etc, than Mint, we mentally discount our potential user number as some percentage of Mints (or Dropbox's, or pick your success story)

When doing such mental math, the larger the successes number, the better you like it. Say your niche is only 5% as large (Mint's niche was pretty much "anybody with money and a computer). So, best case, you're looking at 5% of Mint. If Mint is only 1.5M, of which, probably most were non-paid ... You get my drift.