1.The typeface should be clear. We want something that is not complex and stands out.
2. It should be clear that there are two words in the name. Foursquare was successful in using different colors to separate both words (just an idea)
3. We don't want people to overlook the 'r' and think the name contains the word 'date' instead of 'dater'. Nothing needs to be done to specifically highlight this letter, but it's worth keeping in mind in case you were thinking of using a thin font that could cause the 'r' to be missed at a glance
4. Logo should display Web 2.0 elements (vibrant colors, possibly a subtle 3-D feel, bold type). Please consult the following examples which have successfully utilized this style: skype, foursquare, hashable
5. Nothing overly cliche (e.g, no large hearts, pictures of cupid, a male & female avatar embracing)
6. One possibility - though I'm not a designer so don't feel constrained by this: Possibly integrate a check mark to represent a user indicating their interest in another member. (Similar to the experience in grade-school when a girl would pass back a note to a boy and it would read: "Do you like me?" with two blank check marks next to the words "yes" and "no" - Please don't include a letter with this text in the logo - just trying to get you thinking about the general concept)
Have fun and let me know if I can provide any more details!