So that is about 10% increase in 47 days. Around 16 August 2015 4M wallets and around 3 October 4.4M wallets.
If you put the curve on exponential it appears fairly flat which I suppose is a good sign - indicating possible future exponential growth.
There are many many variables here (I suppose many people create multiple addresses) but it does appear to be picking up speed which is a good thing.
Where this number comes from?
Is it the number of unique addresses with non-zero amount?
Or may be this is a number of registered emails on some online wallet like bc.i?
I have several wallets there (no more than 10, but more than one) but do not remember details (no funds on each account)
upd: oups. i see you are talking about bc.i