Is this a job that will have a long-term effect?

Holidays are a good time for reflecting on what we do. Over the past week I have been doing a bit of contemplating education and Doug Johnson's question in his blog about time really got me thinking.
Do I as a teacher have a long term effect on my students? It is obvious from reading biographies and histories that teachers can have an influence on their pupils eg Helen Keller. In my own life there were three key teachers who enthused me, Thanks Mrs Seaman, Mr Shepherd and Mr Lovell. Talking to other teachers at a training day from Julia Atkin many teachers sited a good teacher as one of the reasons they got into teaching.
Having only taught for six years it is hard to determine the long term influence of what I have done but a number of my students who i have stayed in contact with on mySpace have said that I have assisted them. One in-particular (when I was having a week teaching despair last year) has sited my continual encouragement in year eleven and twelve chemistry as the reason she was able to get into and do the university course she has just completed. Come to think of it perhaps the fact that I am a mySpace "Friend" to over 100 current and ex students shows that I have an influence over them. I think the key is to ensure that that influence is a positive one that encourages exploration of knowledge, creativity and safe behaviour.
David