I have been asked a lot about this. Read on here to know the DETAILED lowdown: http://cru.cahe.wsu.edu/CEPublications/FS163E/FS163E.pdf
Only want the brief? Here it is, quoted from the above link:
Rubber mulches can be attractive, easy to find and apply, and may not need frequent re-application. However, there are significant problems associated with using these mulches. In the short term, rubber mulch is not as effective as other organic mulch choices in controlling weeds. Furthermore, rubber mulches can attract insects (e.g., cockroaches), and they are highly flammable. In the long term, decomposing rubber mulch releases heavy metals and organic chemicals with unknown effects on human and environmental health. Other organic mulch choices, especially wood chips, are better performers and pose none of the environmental risks attributed to rubber mulch.
Personal note: If you are near weeds, the seed will still germinate in the rubber mulch. I vote no for this product. I have tried it and regretted it.
