Steps to reproduce:
1. Open a larg document, say 4 MB, 1000 pages
It's so slow that practically is unworkable, while opening the same .odt with MS Office 2010 the document opens as quick as a wink, and you can edit and work with normally.
Be able to normally edit your document
Platform (if different from the browser):
Browser: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/536.11 (KHTML, like Gecko) Chrome/20.0.1132.43 Safari/536.11
The *loading* or the *editing* is slow ?
If its the editing, *and* the OS is Linux *and* the fonts used in the document don't exist, this may be a duplicate of bug #47636. If it is then that theory can be tested by ctrl+a and changing the font to one that is installed. If that makes it fast again this will be fixed in 3.5.5.
OK, I think I've got it. It's when opening a .odt file which is located at a NTFS partition in Ubuntu. I've moved it to /home (ext4 filesystem) and works fine. Sorry for all the trouble :(
Marking as NOTOURBUG, it very well could be an issue with NTFS utils if you're having a problem on your NTFS drive. Thanks for the update