If you use the latest BSD released version then you're ok. The code is free for public use. Were you to make it commercial though I think you would be liable as you would need the explicit permission of the original owner to do so.
EDIT: It seems after further research the license that was being used prohibits the name "Growl" being used to promote any derivative works of the same name without explicit permission from the original owners.
[1] - http://growl.info/documentation/developer/bsd-license.txt
Were you to make it commercial though I think you would be liable as you would need the explicit permission of the original owner to do so.
Just about every open source licence, include the BSD released code, explictly gives you the permission to sell the software. If the original author released Growl 10 years under an open source licence then they gave you the permission to sell it commerically then.
The name is complicated and usually falls under trademark law, and hence you probably could be sued for claiming that your fork is "Growl" when the average person thinks that only $ORIGINAL_AUTHOR can release "Growl".
EDIT: It seems after further research the license that was being used prohibits the name "Growl" being used to promote any derivative works of the same name without explicit permission from the original owners. [1] - http://growl.info/documentation/developer/bsd-license.txt