Here is the final suggestion from Kedaman, adapted a bit:

- new member 0-16
- junior member 17-32
- member 33-64
- lively member 65-128
- addicted member 129-256
- hyperactive member 257-512
- fanatic member 513-1024
- guru 1024-4096
- ?Wait and see? 4097+

I'll be putting that on in the next few days.

John