Well, high-trafficked Websites such as slashdot, Amazon, and may others do quite fine with Perl every day. As many developers discover over time, the primary issue with performance and scalability is whether or not your tech people are competent. If you have questions about their competency, it can be very easy to build slow, hard-to-maintain Web sites in any language. In fact, Perl may be worse than others for this because less experienced developers don't know how to harness its power.
However, if they're competent, Perl can be a fantastic choice because of how easy and fast development is. Much of performance comes from things outside of the programming language. Do you have competent DBAs? Decent load-balancing? Are you dynamically generating pages with static content? Do you understand how your site is going to be used and know what to target for profiling? How's your network set up? Do you have media servers separate from database and app servers? Heck, if you feel you don't need stuff like that, you probably won't have enough traffic or usage (not the same thing), to worry about whether or not Perl is a bottleneck.
In short, performance and scalability depend on many factors, not just Perl. (Side note: I've done a lot of work with "enterprise" level Perl in high-demand environments. I have no problems with it)