Social content discovery service StumbleUpon has surpassed a monumental milestone after users hit that big ol’ Stumble button more than 1 billion times in March. That’s a whole lot of procrastinating. I mean, finding interesting content.

The news was announced on Twitter Wednesday by StumbleUpon founder and CEO Garrett Camp. Taking a look at a graph which displays the number of monthly stumbles shows remarkable growth — the service has more than doubled the number of stumbles per month since July 2010. At the time of this writing, StumbleUpon has 15,442,285 members.

Social content aggregators appear to be in the middle of a boom period, with Reddit surpassing 1 billion monthly pageviews earlier this year and hiring more staff following a hugely successful period. StumbleUpon’s stumbling milestone came in the same month that it raised $17 million in a Series B funding round.

While Reddit and StumbleUpon are performing well, Digg — a service which was at the forefront of social content curation — has been in a tailspin since launching version 4.0. Digg’s downfall has been so spectacular that, despite attempting to win back users by adding more features to the service, even its founder Kevin Rose has moved on.

[Image Credit flickr, mager, Twitter, @gmc]