What office suite will be used in 11.04?

Which office suite will be used in Ubuntu 11.04? Open Office or LibreOffice?

Debian and Ubuntu have been using the Go-OO patched version of OOo for quite some time (e.g. the website link for OOo in Software Center points to the Go-OO site), and according to the Go-OO frontpage, Go-OO will be discontinued now that there is The Document Foundation / LibreOffice:

Go-oo joins forces with LibreOffice

Go-oo shares much of its goals and philosophy with The Document Foundation's LibreOffice project, we're therefore supporting LibreOffice since it's inception, and are in the process of merging most of our patches over, as well as migrating to Document Foundation infrastructure. Going forward, the Go-oo project will be discontinued in favor of LibreOffice.

Currently LibreOffice is upstream OOo (= Oracle) + Go-OO patches (mostly Novell) + some other various patches.

So if LibreOffice 3.3 is released in time for Natty, I guess there would be no point in releasing anything else—releasing standard OOo without those patches would result in a serious loss of functionality. (Of course, if Oracle agrees with that, it could still be named OpenOffice.org like now, but I somehow doubt that will happen...)

If I remember a UDS session correctly someone from the Desktop Team told me that LibreOffice will be shipped in Natty.

It is Libreoffice. For more on Libreoffice and Ubuntu, please take a look at the Ubuntu wiki page.