Why keep contact through Hypertope if I already have all my contacts written down in my address book?

The simple answer is that academic contact details do get lost as they change very frequently.  Academics and research students are very mobile people and constantly move between universities and therefore frequently change their e-mail addresses.
Imagine a scenario whereby the e-mail address of one of your academic acquaintances has changed.  In this case your address book or your business-cards album won’t help.  However, if both of you are on hypertope you can keep contact in a much easier way because you can change your e-mail address and other information whenever you need.

Imagine a scenario whereby you meet a researcher at a conference and would like to keep contact in the future.  And so, you exchange business cards or write down each other’s e-mail addresses in your diary.  Few months later you write an e-mail to her, which bounces back because she has moved to another university and has not informed all of her extended contacts about her new e-mail address.  So the contact is lost, and it will take a while before you can find her current e-mail address again. 
Also imagine a reverse scenario whereby your main e-mail address has changed and you have to notify everyone you have met and occasionally keep e-mail contact with, about your new e-mail address and your new university and so forth.  It’s most likely that you will notify only a small circle of colleagues about such a change.

However, if you change your e-mail address on hypertope, then the next time someone clicks on the “E-mail” tab on your page he/she will be able to send you a direct e-mail to that address.  And what is really handy is that your e-mail address is not visible anywhere on hypertope, which is a great way to prevent spam-bots from detecting your e-mail address.
In effect, your hypertope page is like your flexible e-business-card which you can change anytime you like.  What is also useful is that hypertope helps not only keep contacts with your academic acquaintances but also be updated with their recent publications, their current research projects, and various other forms of dynamic information like the conferences or workshops where you may meet again.