NEW YORK (CNNMoney) -- Facebook surpassed 900 million active users last month, according to a regulatory filing, helping the social network post more than $1 billion in sales in the first quarter.
But the company's growth rate, though still staggering, continues to slow. Facebook's monthly active user count -- the number of users that engage with the site at least once a month -- grew by 33% in the first quarter over the first quarter of 2011. A year ago, the network was growing at a 58% annual clip, and in the first quarter of 2010, that number was more than doubling.
Facebook also noted last month that it believes approximately 5% of those users are fake.
Still, for a company approaching 1 billion active users, a 33% growth rate is nothing short of impressive and is likely to fuel more interest in the company. Facebook's eagerly awaited initial public stock offering is scheduled for May.
Facebook said that it earned $205 million in the first quarter on $1.1 billion in sales. Both revenue and profit fell from the fourth quarter of 2011, which Facebook chalked up to typical advertising sales slowness in the first quarter compared to the fourth.
"We believe that this seasonality in advertising spending affects our quarterly results," the company said in the filing.
Though sales grew by 45% over the first quarter of 2011, net income was also down 12% from the first quarter.
Meanwhile, the company's closely-watched cash hoard remained virtually unchanged in the first three months of the year from the $3.9 billion it registered in the prior quarter. That's despite adding 339 employees last quarter, growing its headcount by 11% -- growth that it said it anticipates sustaining "for the foreseeable future."
The company said it forecasts capital expenditures of up to $1.8 billion in 2012.
Facebook went on a spending spree in April. Earlier Monday, Facebook announced it had purchased a portion of a large patent portfolio for $550 million that Microsoft (MSFT, Fortune 500) had previously bought from AOL (AOL) .
It is also forking over $300 million in cash as well as $700 million more in stock to purchase mobile photo sharing startup Instagram. The 23 million shares it plans to give to Instagram appears to value the company at about $75 billion.
Facebook's stock is expected to begin trading sometime in mid-May. By then, most analysts estimate Facebook's valuation will fall somewhere between $85 billion to $100 billion. 
