In teh case of a very long thread (such as in the sticky 'Operation Isa needs Postcard) you can jump to the last post quickly but you can't jump back to the first post.
Last Post/First Post
Usually you just have to click on the page 1 link. If the link to page 1 isn't there, then I suppose it isn't all that easy. But that seems a rare(ish) situation. Do you want to just always see a page 1 link provided?
You know what it is? The link to page 1 stays there as long as you're just hitting 'Next', but as soon as you go 'Last Post' it disappers
The issue actually occurs whenever you move past the 7th page of a thread (or a forum / photo gallery for that matter).
I've created a fix for the issue, so a page 1 link will always be available. You will have to wait till our May 1st reboot to see this live though 
[ Edit: Fixed link... ]