v-strings. Horrible idea, badly implemented, and the cause of many unforseen consqeuences. TIMTOWDI gone stupid.
pseudohashes. Another bad idea implemented poorly. The actual usefulness of these is minimal, and places where they can be used *correctly* are usually contrived examples. More TIMTOWDI gone stupid.
global $|, $/, $\, etc.. instead of per-filehandle.
I agree with Dominus about strigified references. Although I admit to printing them just to see what's inside sometimes... that could be fixed by tinkering with print instead of strigifying things. Laziness gone horribly awry.
$ used on single elements of hashes and arrays.
<> globbing
And probably more that I can't think of at the moment, it's been a long week. For a *real* thread-burner, ask me about those features of perl that I *adore* that everyone else hates. :)