I've taken 4 birding trips with RS, and the one to Chincoteague (staying at Chinc Field Station) in May was the best one!  The staff at the field station were great (and good birders too!) - they changed our itinerary at the last minute to go to a great meadow area instead of going to  2 sites which had similar species.  We saw some really great birds on this trip.  I got 4 lifers, including a gull-billed tern.