I guess that would depend on the content of the thread, certainly useful for long posts with a lot of technical information where you would need elsewhere.

Can't see myself printing out a bunch of threads on regular basis though.

Printer version = Duplicate content issues alert.

add the printer version to robots.txt.

I only print out maps and recipes. Lyrics get printed too but regular forums? nah. Bookmark is good enough.

Yes, I was thinking on putting printable version for logged-in users only to avoid duplicate penalty. But now it seems it's not a very useful feature (unless you travel frequently and want to print something out while on flight, for example).