yes. and as in the past the upgrade warning is, if you depend on your jailbreak. do not upgrade. 4.0 will be released on monday, it will require itunes 9.2.
do not upgrade to either if you want to continue to jailbreak in the future.
iOS 4.0 will be released on 6/21, it will require iTunes 9.2. if you wish to continue to jailbreak
DO NOT upgrade iTunes or your device until it is declared safe by the dev-team. follow
http://blog.iphone-dev.org/ for more information.