Hi Mitla2k5,
First of all, I would like to confirm that based on your tags and your description, you are using Office 365 Enterprise plan after the service upgrade version. If this is not right, please provide us with the correct information. Otherwise, please continue reading below.
Robert is right, the slowness could be caused by the servers being busy due to the upgrades and conversions during that period.
Since your account has just been upgraded, kindly give it 24 to 48 hours for your account to be fully provisioned. If after that period and you still experience slowness, please provide us the following information so we could further investigate.
1. Which specific part or feature of Office 365 or which application are you experiencing extreme slowness?
2. How long has it been since your account was upgraded?
3. Your Operating System (also please indicate if 32 bit or 64 bit).
4. Your internet browser version (also please indicate if 32 bit or 64 bit).
Thank you,
Paul Banez