Spreadsheets - Gnumeric works great, I use it frequently. AbiWord - New version on the way. Presentations - ? There was at one time a plugin for Evince on the desktop that permitted it to view PPT files, thought I don't know its dependencies.

Contacts/Calendar/Todo: it's a solved problem, including synchronization: http://cleardefinition.com/page/Sync...d_GPE_on_N800/ If you just want to use it on the tablet, you just need to get GPE. The rest is if you want to synchronize it with a Linux desktop program.

Hope this helps! You might also want to search the forums for your needs, as I've posted these links before and such. Lots of knowledge already recorded in the forum.