To those having trouble can you update to the latest version of Safari?
I have Lion on my MacPro and Snow Leopard on my laptop. It is on that fine line of being compatible (core2 duo from 2007) but first it will require more memory at the very least. So I have both worlds, plus an iPad 2 and iPod touch 2. A mix of old and new. My iPod touch is out of luck since I pretty much upgraded to iCloud immediately and no longer have the benefits of MobileMe for syncing calendars etc. that device. Sacrifice and compromise is what life is about. However my laptop was able to upgrade to the latest Safari (remember, still Snow Leopard, old laptop) I can go to iCloud.com (on the latest version of Safari and I could log in as well using the latest version of Firefox) and have my calendars and other iCloud stuff available to me. So while it isn't in the Calendar app itself that I can post new events on the website from that laptop, it still works. And pretty much looks just the same as the Lion apps. The bottomline is that I can do updates, just not where I was used to doing it and I can share the online calender and subscribe to it in my old Calendar app and it all updates anyway.
I do agree that MobileMe worked just fine for me and I personally was very happy with it. The new iCloud and Lion have their issues, but I have pretty much been able to find work arounds, but still some things will not work as they did. However I find that to be true of most things in the modern world on a constant basis.
Also it does seem Apple is working on providing iCloud for Snow Leopard (checked out the link posted up thread) so my suggestions are a stop gap until then. And I did it using a computer running Snow Leopard, however it is an core2 duo processor, not sure if anything running a PowerPC chip would work, would depend on if it could run the latest browsers.