Not really. If a person answers your queries and you wish to keep a future eye on their activities then you add them to you favourites. There is no compunction to communicate with those people. With Personal Messages, it is just a way of speaking to someone about something you do not wish to be public, for instance if you are giving your address or asking for seeds etc.

glad thats cleared up didnt want to add a favourite in case it was refused---bearing in mind i have just joined so im a bit on the dark side as to how this site works

If someone makes you a favourite, you don't get a choice about it, Deckingman, lol, it just happens anyway. If you make someone a favourite, you get notifications in the list at the bottom under News on your home page when they've posted something - a blog, a photo, whatever, so you can follow what they post.