I think perl (especially in combination with XS) can do nearly everything. But some things don't make sense because there exist faster solutions, e.g. 3D programming (Corion showed me at the last frankfurt-pm-meeting that it can be done, but it isn't very fast; a 3D shooter like quake wouldn't give enough frames per second to be comfortable enough on a common PC) or system drivers.

Btw: Perl/CGI usually seems to be a little bit slower than ASP, but you can probably use mod_perl. And comparing Perl/Tk to VB is a bit like comparing oranges and plumns, since AFAIK in VB you can only use objects, whereas in Perl you can create your own ones (may have changed with .NET, I don't know). And often, the VB-GUI looks more like a windows application than Tk where some widgets look ugly, e.g. Tk::Notebook or Tk::Combobox. But if that is essential, you can as well use wxPerl instead of Perl/Tk)