Since we released the Beta version of Sampa at the end of May, we had at least 1 sign up per day every day. In the middle of June, it was at about 3 sign ups per day. Then, on July 31st everything changed when CNET News.com run an article about Do-It-Yourself web, where the featured company was Sampa. That same day we've got about 1000 sign ups, followed up by an appearance on LifeHacker with another 500 sign ups.
After that we had many other mentions on popular blogs (not on TechCrunch yet) and the sign ups have been all over the map, from 50/week to 500/week.
On the the past 2-3 weeks the average has been 50/week (5-10 per day), but this week we've got 115 sign ups. It is not outside of our expected range, but it is unexplainable. What I mean is there is no big article anywhere, the referer source doesn't show anything new, so we don't know where the users are coming from.
Actually, we have a clue, except when we have this big articles that attract thousands of visitors to Sampa.com, about 50% of ours users come to Sampa.com without a referer, which means they either received a link by email to Sampa.com or they typed/bookmarked the link in their browser.
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at the end of May, we had at least 1 sign up per day every day. In the middle of June, it was at about 3 sign ups per day. Then, on July 31st everything changed when CNET News.com run an 
January, 2008