Sorry to be vague. I'd use it as substitute for a login mechanism.

Instead of a combination of username and password where the username is the internal identifier, I'd use solely a BTC address. For the login a random one-time-challenge string is shown to the user and he or she is asked to sign this string.

Example:

System: "Please sign the following message: login2113njsdfku3h24"
User answers with: G42O9cr+bwzfH71zfmFjIy/UmuQhVOxmqm5HgBglHMK/ceKCKBWSmLLd9sz8ZXpJxtAN0xwbyLyCwRjuUiQ7i/c=
The system verifies the signature and maps it to address: 17mDAmveV5wBwxajBsY7g1trbMW1DVWcgL

This address can then be used to recognize the user like the username before.

Hi all,
because everyone seems to play but me and another user get only a error,
i decide to clear again Cookies, cache etc.
after/since that (or just in this moment ?) PD was unreachable.

Is this only for me or down again ?

Thanks in advance