QBasic, and also writing DOS batch files. I've also given up DOS, Windows, and television, but those are things I gave up for other reasons, not because of Perl; whereas, giving up QBasic was directly the result of learning Perl.

I would have given up batch programming later, when I gave up DOS and Windows, but in that case I probably would have had to replace them with shell scripting, if not for Perl. As it stands, I gave them up sooner, while I was still using DOS and Windows, and when I switched over to Linux (and now FreeBSD) I have never taken up shell scripting. I don't need to write shell scripts, because I speak Perl.

I've also given up on Python and PHP, both of which I tried to make myself learn sometime after taking up Perl. They didn't take. I do still mean to try Ruby at some point. The way I figure it, I'd better learn Ruby soon, before Perl6 really becomes practical, or otherwise I'll never get around to it.