Hi,
I use(have always been using mac´s) in my work. I work within molecular biology and rarely find a program not encoded for mac.
Most imaging and structure analysis software (imageJ, "O", deconvolution programs etc) work perfectly on a mac. As does the Adobe programs of course. The only SW that is annoyingly not compatible with mac is ZEISS LSM software for microscopy but imageJ can sort of circumwent that obstacle.
What sort of science do you do? Feel free to ask about specific applications you consider running.
/Kalle