1Peel each grapefruit down to flesh, leaving no white pith. With sharp knife and between walls of membrane, cut segments straight down. Gently remove sections. Squeeze remaining membranes to extract juice; set grapefruit segments aside. In small bowl, mix reserved juice, vinegar, honey, shallots, thyme, salt and pepper with whisk; slowly add oil, stirring constantly with whisk.
2In large bowl, toss lettuce with grapefruit segments, pine nuts and desired amount of dressing. Serve immediately. Refrigerate any remaining dressing.