Apple’s iCloud.com site is now open for business allowing you to sign and access the service. Of course until you get your device upgraded to iOS5 (coming later today) it won’t have a lot of content on it.
Available online will be copies of your Mail, Contacts and Calendars, and also copies of your iWorks documents you have backed up to iCloud. Also, presumably, an icon will appear for your Photostream that will be shunting all your photos around between all your iOS devices.
However things like Find My Iphone are now working and available via the website centralising the services into a neat control panel interface.