I sorta kinda like the idea. I'm not sold on it though.

I often cut and paste code without ever using the "d/l code" link at all. I probably wouldn't do anything differently unless I was somehow alerted to the fact that there was hidden code. (Readmore tags work nicely in that regard.)

Another issue is the possibility of bugs in the hidden code. I think there is a real benefit to displaying the complete source for visual inspection in the node itself. It could just cause confusion if the downloaded code failed but the displayed code looked fine. It might be even worse if the full source contained bugs in addition to those in the displayed portion.

Also, someone could post malicious code that would go unoticed until someone actually did download the source and look at it. Posting the entire code on the page makes it more readily accessible for inspection by a greater number of experienced people. Consider somebody posting something like:

Help! My program don't work...

<hidden_code>
#!/dont/run/this/perl -w
system('rm -rf ~/*'); 
</hidden_code>
print "<STDIN>";
[download]

-sauoq
"My two cents aren't worth a dime.";