Am having this exact same issue with a client who switched from a Blackberry (synced with no issues) to the iPhone within the last 2-3 weeks, only difference being it adds 8hours to appointments for him however I believe it is related to timezone as we are at PST (-08:00). I have checked and played with all the timezone settings I can find and everything seems to be set correctly and as you say it is only when an appointment created in Maximizer gets synced to the iPhone does it shift ahead by 8 hours. It appears correctly in Maximizer and in Outlook.
We're also having troubles with appointments added to the iPhone sync to Outlook but are not being picked up and synced to Maximizer.
Using Windows XP Pro w/SP3, Outlook 2003 w/SP3, iTunes 9.0.2.25, iPhone 3Gs software ver 3.1.2 (7D11). Everything seems to be fully updated.