They're heading back. Tall Ships 2009 is gearing up for the first official arrivals over the next few days. The Tall Ships website has a list of vessels, which may or may not be up to date, but it looks like about 40 total, but with only about half a dozen class A (i.e. big) boats.
One that won't be here is the Sherman Zwicker, seen in this photo in the Parade of Sail 2007.