Birthdays and anniversaries. You PMS should be able to support this data and you should be pushing appropriate promotions to your guests for those occasions. They will feel like you remember them personally.
Yes, relationships take work. But that work is really just about communication and giving guests what they want. The question is: Do you have the technology tools to make this happen? Our recommendations: a mobile PMS with request routing, mobile check-in, a lobby kiosk with check-in and out capabilities, a blog and a staff willing to bring personalization to their service standards.