Oh my effing god, I cannot believe this mercury bull**** is STILL going around. Thimerosol hasn't been used as a preservative in /any/ vaccine intended for children since 2001. Small amounts of mercury are contained in thimerosol in multi-dose bottles, yes. The amount contained has been reduced greatly compared to what was used 10-15 years ago. You'd get a bigger dose from eating a single meal of fish. It is NOT biologically available in the same way that methylmercury (what actually causes neurological side effects) is. If you are still nervouse about it, single-dose versions are available.
Vaccines do NOT cause resistance in bacteria/viruses the same way that overuse of antibiotics does! The seasonal flu shot contains dead virus particles from the three most commonly seen strains in the southern hemisphere. Generally, seasonal flu spreads upwards from there since their winter occurs during our summer, and provides enough lead time for scientists to identify the strains and to develop the shot available to the northern hemisphere by the time winter rolls around up here.
I can understand people not wanting to spend money for something that is not 100% guaranteed to work (since there are technically hundreds of strains out there, and if you wait long enough, you may already be sick with flu before the two week mark when your immune system has made the virus-fighting antibodies). If it is free or already paid for by your employer or insurance though, and you DON'T have an egg allergy or aren't pregnant, then why the heck not?