To answer your question I think you need to look at two things.
1. prior to the "silicone crisis" of the early 90's, 97% of implants used in the United States were silicone
2. in the rest of the world (where both saline & silicone have been continuously available), silicone current holds 95-98% market share
Implant manufacturers are privately projecting at least 50% market share for silicone by next year and 70-80% after that. What the upper ceiling is remains to be seen, but I bet we're going to be using 90%+ silicone within 5 years & I think the form-stable implants (Inamed's 410 & Mentor's CPG) will dominate a few years from now as the rupture rate is so low (at least thru 6 years, ~ 0.3% on the only literature on this). Right now, I think cost will continue to be an issue that may make the price-sensitive group more likely to pick saline. OTOH financing is so simple right now that $1000 difference is pretty insignifigant over a 3-5 year period