sure, the number of softwares being available for a mac is increasing, but that is mainly true for general softwares. most programs used in research (mainly in the sciences, i don't know in other fields) aren't usually available in mac. and the ones that are cut a deep hole in your pocket. i saw that you are in 'biological sciences', and from the perspective of a geneticist/systemicist/population biologist/ecologist, i can say that mac is not the smartest choice. i do use mac and unix boxes in our lab because the department bought them for us, but they have less than 10% of the total programs i run. as some people said above, if you run a lot of windows based programs, then getting a mac isn't really a good idea. you don't want to make the trip all the way from your home to the lab just because the program you want to use is in the pc in your lab.
in your case, you can simply get a replacement battery. also consider the new lenovo thinkpads.. they look loaded. if you want to switch platforms, the main problem you will have is getting used to the new system, but this won't be much of a problem. if there are certain programs that are mac-specific, you might want to look at how to dual boot your machine with a unix OS. most developers who release programs for mac also release unix/linux versions (at least in biology).
as for those who think macs don't get infected by a virus, that isn't actually true. the frequency of attacks is super-super-low. but the idea of macs being invulnerable to viruses is a myth.