Modul8 has been one of the premier VJ applications for Mac OSX since version 2.0. Following is a review based on extensive use up to the latest version, which as of this review stands at 2.5.2.
Pros

• Ability to use native OpenGL Core Image and FreeFrame plugins.
• Extensible, highly-programmable user interface.
• Excellent keyboard and MIDI mapping.
• Can use multiple video cards to span video across multiple screens.
• Good learning curve.
• Plenty of preview options.
• Frame-accurate rendering to disk.

Modul8 offers ten fully adjustable and scalable layers to composite and position in a variety of different ways. The best thing about Modul8 is that its geared towards transparency and ease of use. It wants to be instrumental and based on playing, not thinking. I enjoy mixing with Modul8, not just the end result, I dig the process of getting there, too.

I'm not saying this is 'right' but this is what i believe:

Style is king: As you experiment, find what works for you and develop it so your show has a unique look - preferably one that doesn't look like anything the punters get at home. I find that the manner you alter raw materials contributes more to this than the choice of what those raw materials are.

Creating your own content. Visual awareness and composition. Part 1

This article is aimed squarely at those people who wish to take their visual material beyond the rip and stitch approach that seems so popular in our field. We are, of course, entering into the realms of the subjective. I.e. there is no black and white here, what stimulates one viewer may be completely lost on another, and neither can claim to be right, this includes myself! I can only speak from my own experiences as a professional artist of more years than I care to ponder.

Creating your own content Part 2

OK, lets play around with that card mask mentioned in pt 1. The key to success in these exercises is in the observation and interpretation. Unfortunately you must do this in isolation, as I can't be there to lean over your shoulder and suggest things, as in a normal teaching situation. However, I'm ok with you sending PMs or e-mails to answer any specific questions.