Email analytics were slow for those of you on the larger side of the subscriber count spectrum. I have written a lot of code (and also deleted a lot of code) to make that situation better: it should take now on the order of seconds to pull in tens of thousands of events, rather than tens of seconds.
There's a lot in store for analytics this year: I'm excited to start pulling in and surfacing web analytics, subscription funnel data, conversion rates, and more. But first, the existing stuff needed to be faster — and now it is.