To the guy that told me that Quicklook creates an image, and hence there will never be a chance of cutting and copying text from a quicklook window, I think you are wrong.
I just quicklooked a text file. If I resize the quicklook window the text re-wraps. So it is quite obviously not making an bitmap image file. Therefore I think it should be quite easy to make it so that a user could cut and copy text from a Quicklook window.
I've just looked at the QuickLook API. The generator can return data in 3 formats (although there are 4 ways): Bitmap Image, PDF or HTML.