Peekabooty is a great concept but :
1) Lots of people are behind a NAT
2)Even more people have dynamic IP's
In number 1) Peekabooty will never be able to submit it's own IP automaticly because it will always send the NAT IP .
In number 2) it won't know it's IP if the ISP rotated the user's IP since the last time Peekabooty ran .
Once the connecting process is automated (by hostcaches for example , look at Gnutella) the program can automaticly determine it's IP by examining the incoming data from the first connection attempts .
Also Peekabooty will be able to automaticly determine if it is NATed or not by comparing the system IP with the reported IP .
This idea really works : Look at BearShare in the Gnutella network . They have been using this for some while now , no complaints yet ...
Try it : www.bearshare.com