Two thousand and seven went out with a bang for IPOs, according to an exit poll released Wednesday by Thomson Financial and the National Venture Capital Association. The fourth quarter's 31 venture-backed IPOs—the most since the third quarter of 2000—brought the year's total to 86 issues that raised $10.3 billion, double the $5.1 billion yielded by 57 deals in 2006. The average IPO offer amount i