Information about the mercury (thimerosal preservative) question is available from the CDC
here and from the FDA
here.
Based on flu vaccine manufacturer's projections, more than 40% of this year's flu vaccines are expected to be preservative-free. The Fluzone flu vaccine is totally thimerosal-free while Fluvirin and Fluarix have only a trace thimerosal concentration (less than 0.000004). Almost all pediatric flu vaccines are thimerosal-free.
When patients discuss flu shots with their doctor, they can ask if thimerosal-free flu shots are available at their treatment center and whether the issue should be of concern to them.