Just played around with a new home router and noticed that my HTC Desire S Android phone sends the following hostname when requesting an IP address with DHCP in a wireless network:
Why is this is a problem? Because the trailing part of that hostname is your IMEI, which is a unique number identifying your device. It’s normally only seen on radio-network level, so can normally be considered “private” (because your operator can’t disclose it to anyone).
The IMEI also contains a component called “TAC” (type allocation code) which identified the exact handset model you have.
So if you regularly visit Internet cafes or the like, these guys know how often and when you are there.
Please let me know whether you consider this a problem or not — I do think it is one.