Simple.Data on Mono is something that people have been asking about, and I've been meaning to sort out, pretty much since the project went from a proof-of-concept to an actual OSS product. One way or another I've never gotten round to it, but a couple of things have made it seem more relevant. Firstly, there are providers for lots of OSS databases now (MySQL, SQLite, PostgreSQL); secondly, a certain @fekberg has been very persistent in his status update requests, so I've taken the time this weekend to make it work.
For the most part, I've been pleasantly surprised by how easy it's been. I've found what I think is a bug in the Mono implementation of either dynamic or LINQ or the combination of the two, which I'm going to file with Xamarin once I've created a simple repro project. I've come up with a workaround involving old-school class-based IEnumerable/IEnumerator implementations, and the performance doesn't seem to be affected, so that's fine.
The hardest thing about the whole process is that MonoDevelop just isn't Visual Studio 2010 + ReSharper. It's not a bad IDE by any standards – I'd still take it over Eclipse any day – but I work day in, day out with VS and jumping into any other IDE just feels like somebody moved all the cheese. Add to that the fact that I'm running it under OSX, so even the standard Windows keyboard shortcuts don't work, and it's a bit like running in treacle. As I understand it, the Mono Tools for Visual Studio don't support 2.10; Miguel de Icaza tells me that they're working on some awesome new VS tooling, so I'm really looking forward to that.
The other big challenge was testing the ADO adapter against a real database. I only own the SQL Server and SQL Compact providers, so I really wanted to test with SQL Server to keep things simple and let me step-debug if necessary. I was expecting not to have fun with this, but it turned out fine. I run my Windows development environment on my MacBook using Parallels 7, so I set up the Host-Guest networking (easy) and opened inbound port 1433 in Windows Firewall (also easy) and that was it. There were a couple of failing tests, one calling a stored procedure with a DataTable and one involving a scalar function, but the rest just passed. I'm guessing that the majority of people who want to use Simple.Data on Mono will be using one of the OSS DB providers, so hopefully this won't be a problem.
I don't know what the Mono NuGet situation is, so I'll be releasing Mono builds as tgz downloads from the GitHub project page. For the time being, there are differences between the Mono build of Simple.Data.SqlServer and the Microsoft .NET build, so if you want to use that provider, don't use the NuGet version.
Right now, there's a 0.11.4 build in the Downloads section which I hope works. However, I haven't really exercised it to any great degree, so if you encounter any problems please raise an issue if you think it's a bug, or ask on the mailing list if you aren't sure.
If you are one of the developers of an adapter or provider, you might want to test against Mono. If, for any reason, that's not an option, then let me know and I'll try to find time to test it for you.
Going forward, I will support (in the OSS sense of the word) both Microsoft .NET and Mono for all releases.