To keep track of the members who are interested or who have already been in contact with you, you can create a list of your favourites.
To do this, just visit the profile you wish to add and click the add favourite link in the top left area.
You can manage your favourites in your settings: settings - contacts - manage favourites.
You can find the number of your favourites and how many of them are currently online in the header of the page
Plus members can also see, who favourised them.