Do you have an Eris? If you open up an email message in gmail, and long press - nothing happens. There are three buttons on the bottom - "Archive", "Labels" and "Delete". Press "Menus" and there are more options - "Archive", "Add Star", "Mark Unread", "Change Labels", "Delete" or "More", which yields "Back to Inbox", Mute", Report Spam". Nowhere is there an option to copy text.
Yes I do have an Eris. My bad though. I didn't realize you were referring to the gmail app, which I don't use. In the regular mail app copy/paste works fine. Seems kind of a stupid move by google not to include that in the gmail app.