High-flying startup StumbleUpon has been rumored to be in acquisition discussions since at least last November. Recently we’ve heard that talks have heated up again, with Google, AOL and eBay as potential suitors. A source with knowledge of the deal now says the company has signed a term sheet with eBay to be acquired. The price is somewhere between $40 - $75 million. (update: GigaOm is now reporting the price at a $40 - $45 million).