[burnout1540]

That sounds like registered users, which may be completely different than active users. The number of registered users tells you very little without also knowing the number of active and/or concurrent users and what type of activity they're doing.

[gt565k]

I agree. Look at engagement rates and how the curve looks on that end. It is much more important than stale users who registered but never used your service/product.

Either way, I'd say a few million users is pretty impressive.

[seekingcharlie]

Agree that total users shouldn't be looked at without % of actives, but he's not asking if it's impressive from the POV of evaluating the business. He's asking in terms of evaluating an engineer who handled the scaling from a technical POV.