Kuki: You're so right...never thought of it that way.
Last night my husband and I decided to go ahead and book a HAL 14 day cruise...(up to now the longest we've cruised is 12 days on Celebrity) just to see how we like a longer cruise on a HAL ship. Since there really isn't any rush to jump into a month long cruise, we'll do the 14 days then maybe 18 days THEN the 28 day.
I have a friend who loves cruising, and had only done seven days...sailed a 10 day and hated it, seven was the magic number for her. For us, after seven day cruises we tried a 10 then a 12 day and now seven day cruises are just too short. We're hoping that our magic number isn't 12 days!