We here at Xamarin are as excited as you are about the release of Lion. But unfortunately we're not quite ready to support you on Lion yet, and MonoDevelop doesn't work quite right. We're working around the clock to make MonoDevelop work perfectly on Lion, and we'll let you know as soon as it's ready.
Update on July 29th: We have most of the fixes in place for Mono and will issue a build for testing on the Alpha channel soon.
Posted on 20 Jul 2011