Hi Beat,
Thank you for your post. I found the Hi firstname choice, but here's the crunch:
1) to be able to use it I need to set the Name style field in the Configuration file to "First and Last name field", right?
2) But then if I do this, new users cannot register because even though they fill their first name and surname in the registration page, they get an error message saying "Please enter your name" and registration does not proceed... And the only way I found to get rid of this error is to set the Name style field back to "Name" but then, I have to greet users with Hi [Name]...