That's a fairly easy one. According to the Las Vegas Convention & Visitors Authority stats, as of December 2007, there were a total of 74,600 rooms on Las Vegas Boulevard. (If you include what they define as the whole "Strip area," which factors in the likes of the Rio, Palms, and Gold Coast, but not the Hard Rock or Hilton, that figure increases to 99,800.)
By the end of 2007, the Stardust and the New Frontier had already been consigned to dust, resulting in a net loss of 2,536 rooms (1,552 and 984, respectively) to the Strip that year, offset on Dec. 28 (so just scraping into 2007) with the opening of the Palazzo, which contributed 3,068 new rooms to the balance.
Encore, the new Wynn tower that was originally slated to open in early 2009, but is, uncharacteristically for Las Vegas, ahead of schedule and now due to open in December of this year, will add another 2,034 rooms to the count.
Your question omitted reference to the Trump International Hotel & Tower, which debuted March 11 and currently comprises 1,232 hotel suites and 50 penthouse suites in addition to the condominium residences, which also need to be included.
So, to answer your question, 6,384 rooms will have been added to the Strip by the end of 2008, offsetting the 2007 loss of 2,536, to result in a net gain of 3,848 rooms for the period in question.
