Winglets will be installed on 28 738s, 10 73Gs (737-700), 10 757-200, and 15 767-300ERs:

http://biz.yahoo.com/pz/070618/121552.html

The 28 738s will also be the ones to get the Song-style AVOD PTVs starting later this summer; they will also have 10 additional seats added though apparently with no perceivable change in legroom (with new Y seats); these 738s will now have 16F and 144Y seats (instead of the current 16F134Y).

Also, not mentioned in the article, but the 15 763ERs with the winglets will be used for longer flights (like ATL-LOS, JFK-TLV, and even LAX-Asia (as Jim Whitehurst inadvertently disclosed during an interview at the Paris Air Show) and will have the lie-flat pilot rest seats installed....I've noticed that they have now worked that into the seat map as every 763ER BE cabin now seems to have seat 5C blocked out as well (in addition to 6C which has always been blocked as it is the current pilot rest seat)...