If you don't migrate from MobileMe to iCloud before June 30, 2012, you will lose your e-mail address.
Unfortunately unless you update from Snow Leopard to Lion, you will not be able to sync contacts and calendars etc via iCloud, but you will be able to use iCloud mail.
Although you cannot sync contacts and calendars via iCloud, you can either access them through your web browser at icloud.com or sync via iTunes instead.
Nothing in Apple's documentation said that contacts would be lost when transitioning to iCloud on a non-supported platform (in this case, Snow Leopard). I've seen others that say that we should have access to our contacts.
Since Mountain Lion is not even in the App Store yet, why would Apple force a migration that required Lion?
I still believe that contacts should be available - it's inconceivable that Apple would do otherwise to long time Mac users.