Hhm.... Since you do this often, well it might help for your current problem, but you couldn't be asking other people to ungroup for you on a long term basis. If you're in a time crunch, let us know, and one of us can ungroup for you.
But what you really need, to avoid this in the future, is a way to convert your files, so that Inkscape can use them, without creating groups out of everything. It looks like it groups everything except text. Hhm, or did you make the groups? If you make the groups, then the answer is simple - don't make groups.
Yeah, but it shouldn't be taking such a long time to ungroup. I think that needs to be solved before we move on, because even though there's a bug report that seems to fit, there are no reports of taking 30 minutes or more.
If you're in a time crunch, let us know, and we'll make you an ungrouped file. And meanwhile, I'm going to try and look deeper into the file for another explanation.
Edit
No, I don't think the problem is ungrouping. Everything ungrouped for me in a flash! I think there's something else going on.
When you were trying to ungroup, which particular object was getting stuck? Which one? Or were you ungrouping all at once (select all > ungroup)?
If you were always getting stuck on one group, can you try a different group, and let us know what happens?
Have you seen this in any other files, or does it seem to be just this one?
Oh, I might be onto something already. Now Inkscape has frozen on me! As it turns out, I had not ungrouped everything yet, and when I tried to finish ungrouping - freeze!