there're some good reasons to ask you to register:
1. We should know the number of "active users" to plan the number and bandwith of our download/update servers. Nearly all active users and a lot of unregistered "trials" are updated in 4 hours - could you imagine the number of requests and bandwith - e.g. yesterday we sent over 40Mbits/sec in some moments.
2. We like to know the origin of the user to find which language should be in the queu for translation.
3. We like to know the E-mail to send the emergancy information. Usualy it's used to inform users about the reregistering. But it can be used to inform about the important upgrade, which isn't done automaticaly.
4. We like to know, where do you find information about avast!
From this points you see, that we need this informations:
1. E-mail - we don't use it for spam, we don't sell them
2. Country of origin
3. Source of information.
All other fields in reg. form are optional...
I believe that it's a little bit more clear now.