Perl 5 solutions will still be useful in Perl 6.
Maybe not. Module and algorithm advice will remain valid, but many people come looking for code snippets. Very basic things like the syntax will change in Perl 6. The elder monks will have no problem reading old and new code and telling them apart, but beginners will be confused if some nodes write $a and others @a . So it has to be made clear what version the node is talking about.
Of course, since Perl 6 is not exactly imminent, neither is this problem. (Things may be different with Parrot which is maturing faster).