Well, one thing about them that might catch some by surprise is that a here-doc comes in two pieces and those two pieces can end up pretty far apart. Take an example:

print <<FOO, <<'BAR';
Usage: $0 [arguments]
FOO
This program doesn't do much.
BAR
[download]

If here-docs were just like strings and didn't come in two parts, then you'd want to write that more like:

print <<FOO
Usage: $0 [arguments]
FOO, <<'BAR'
This program doesn't do much.
BAR;
[download]

which doesn't work. You can write it like this:

print <<FOO
Usage: $0 [arguments]
FOO
, <<'BAR'
This program doesn't do much.
BAR
;
[download]

but I think the first example is easier to read.

        - tye (but my friends call me "Tye")