Is fantastic, I have had one for ages and its not too hard to maintain.
1) shirt off times = you get attention. Simple as that, just as a girl with a slim waist and large breast in a bikini would get attention.
2) "Please can I/we see your 6pack again" - once a girl found out you have one but you don't get it out at every opportunity, women ask to see it or take your shirt or whatever. Great ways to make them qualify etc etc. Honestly, it happens.
3) Its a great way to feel better about yourself, its no replacement for actually just being confident in your own skin... but even if you are already, knowing you look HOT will only make things better.
4) 90% of girls like 6 packs, a lot. Not only is it physically attractive but ao shows you have commitment (you had to put in a lot of work to get it and to keep it), shows you take care of yourself (its about food aswell as exercise).
Don't forget to do a wide variety of tummy exercises, there are lots of muscles around the abs that are needed to get the really hot 6 pack.
Sit ups, Crunches, leg lifts. All 3 of those with twisting.
Static holds, floor wipers.
There are more, but if you do those you are basically sorted. If you are serious about getting a 6 pack, don't count reps. Keep going until you cant do the exercise with proper form and then rest and do 3-5 sets (until you cant do many reps at all).
Do all exercises slowly and controled, 1 second to do the up motion and 3 to go back down. (obviously not static holds

)
Hope that helps.
Madals