Change view function, and pass request.user to the form
def event_view(request, slug, model_class=Event, form_class=RSVPForm,
template_name='rsvp/event_view.html'):
event = get_object_or_404(model_class, slug=slug)
if request.POST:
form = form_class(request.user, request.POST)
if form.is_valid():
guest = form.save()
return HttpResponseRedirect(reverse('rsvp_event_thanks',
kwargs={'slug': slug, 'guest_id': guest.id}))
else:
form = form_class(request.user)
return render_to_response(template_name, {
'event': event,
'form': form,
}, context_instance=RequestContext(request))