i upgraded my iphone to the 2.0 firmware yesterday since the jailbreak was just made available. sadly, some of the apps i was used to don't work on 2.0 yet (sendpics, mcleaner, etc.) but one of the most annoying changes was that i couldn't easily disable the typing auto-correction with a tweak to the preference plist like i did with the 1.1.x firmware.
however, it seems if you just move the dictionary out of the way, it accomplishes the same thing:
iPhone:~ root# cd /System/Library/TextInput/ iPhone:/System/Library/TextInput root# ls TextInput_da.bundle/ TextInput_it.bundle/ TextInput_pt.bundle/ TextInput_de.bundle/ TextInput_ja.bundle/ TextInput_ru.bundle/ TextInput_en.bundle/ TextInput_ko.bundle/ TextInput_sv.bundle/ TextInput_es.bundle/ TextInput_nb.bundle/ TextInput_zh.bundle/ TextInput_fi.bundle/ TextInput_nl.bundle/ TextInput_fr.bundle/ TextInput_pl.bundle/ iPhone:/System/Library/TextInput root# mv TextInput_en.bundle oldTextInput_en.bundle iPhone:/System/Library/TextInput root# reboot
it doesn't seem to be any faster, but it doesn't correct anything and i haven't noticed any ill effects.