It will mark the start of the Summer of Arcade which begins July 21st. It allows you to sort games by price and rating, and see what friends have.
Destination Arcade is a huge UI makeover for the current way to browse the arcade wares of XBLA, and it's a much needed change over the current system. The latest releases and discounted titles are easier to find and you can sort by price or rating.
"Also remember that if you purchase all five titles, and you’ll receive 1200 Points back," Major Nelson, referring to the Summer of Arcade deals. If you snap up all of the 5 titles then you get a rebate of 1200 MSP.