That growth references traffic, I believe. But by many other accounts they are growing rapidly. I don't think spam/porn is a HUGE problem yet, tho I've seen more following me (@webwright) lately.
I've also heard that their API traffic is 20-30x their web traffic, so when you see their web graphs, that's worth pondering.
The problem IMHO will be the fact that it's reasonably easy to make money from their web traffic. Making money from API traffic seems downright impossible to me.
I've also heard that their API traffic is 20-30x their web traffic, so when you see their web graphs, that's worth pondering.