St. Germain Elderflower Liquer

I just returned from a wknd trip to nyc and we hit several restaurants and lounge/bar places and a began to notice a recurring theme on their cocktail menus - St. Germain Elderflower liquer. It was in everything. I had some amazing cocktails, including a pear cosmo at Bar Boulud, the mosquito at The Rose Bar @ Gramercy Park Hotel and red pepper, red pepper at Pegu Club. All were exquisite. I also saw many cocktails made with lillet blanc, a favorite summer treat for me.

I know very little about St. Germain and am thinking of buying a bottle. I've read a little on the internet. What do you use it in?