According to the Mono people, the VB.Net support in Mono is relatively new. However, they contend that it is totally complete and the VB.Net compiler etc. pass all of their unit tests. That does not mean that there won't be bugs, as with anything.
You should most definitely give it a try. VB.Net has complete support in Mono and it shouldn't behave any differently than it would on a Windows machine (though, as always, no guarantees).
