My comment was in respect to the privacy etc comments as far this was some attempt to steal one's password etc. Unite.geocaching.com and geocaching.com are effectively the same websites, i.e., Geocaching.com
Thats not altogether true.
geocaching.com uses two servers. 66.150.167.149 and 66.150.167.148
unite.geocaching.com is hosted on 66.150.167.136. They are both in the same /24 block, however that is no guarantee that they are on the same host or even in the same city.
As Biggles Bear said, asking for the users password on a form such as that one bad practice. It goes against all that we are trying to to to educate internet users about security and is unnecessary.
It is possible to pass a cookie between a domain and a subdomain. We do it here. That's why your single login works for both geocaching.com.au and the subdomain forum.geocaching.com.au.
If the servers are located in the same building the form could have been designed to authenticate a user in real time against the existing database.
There is nothing to say how the information is being stored. All we know is that there is an insecure web site collecting user names and associated passwords in clear text. The form passes all data to another page called Default.aspx. One could assume that form simply stores the data in a database. Not as attractive as a list of credit card numbers but it could be attractive to some, given that a lot of people use a limited number of passwords over websites.