I love ack, but I'd strongly recommend .ackrc support. For example, one project I work on has non-standard extensions for Perl files, so ack doesn't recognize them as being Perl. It would be nice to have an .ackrc so that I can provide those extra extensions to add on to ack file recognition or to specify default switches. Of course, this would require an extra switch to ack to ensure that the .ackrc is not read, if necessary.
It would be a nice feature for prove, also. The vast majority of time I just type prove -l t. For prove, you could ignore the .proverc if you have any arguments. For ack, you could ignore the .ackrc if you have more than one argument.