I setup iCloud last night from my iPhone and when I log onto iCloud.com I see 2 or 3 birthday reminders for every contact I have. Also, when I go into a contact, some dates like anniversary, show up twice in their contact information. I obviously did not set up their anniversary twice. I use Microsoft Outlook 2007 on a PC and I had trouble with mobileme and that problem years ago, so I never used mobileme.
I also notice that in ios5 some of my calendars don't show up at all. I have one calendar on my phone but it's not showing my other one and on my iPad it's the total opposite. Ironically my wife's calendars show up on my phone and my iPad. It's very frustrating. I don't know if I should start setting new calendar events using iCloud rather than yahoo or gmail to avoid this.