Virtual classrooms - part of your learning & development mix?

While 'on the job' learning remains critical for capability development, the global and mobile nature of today's workforce means learning must be as flexible as possible, i.e. capable of being delivered anywhere, anytime and in bite-size chunks - after all, we are all time poor! Has virtual or online learning become part of the L&D mix in your business? Are you using it for your own development? And if so, what are the critical success factors for learning in a virtual classroom?