Winglets were until recently common on glider designs. The conventional wisdom is that they improve the low speed handling and climbing characteristics, but that the penalty is reduced L/D at higher speeds.
Some recent designs have cranked-up wingtips with complex leading edge changes in the outer third of the the wing. These may or may not have winglets.
Examples at:
http://www.alexander-schleicher.de/englisch/e_main.htm
http://www.dg-flugzeugbau.de/technis...en-1000-e.html
http://www.schempp-hirth.com/en/flug...s_4/index.html