Depends on what field. Granted one can do anything on any platform these days, whether it be virtualizing windows on a mac, or running a hackintosh or maybe a remote os x vm on a windows desktop.
Back when I was working with some astronomers about two years ago they all ran OS X with the occasional boot into red hat because it was compatible with some code that they bolted onto. I'm not sure what the exact program(s) were though. I think its just personal pref.
Now if you ask Apple they lists these examples as scientific software for OS X:
4Peaks by Mekentosj
Bioinformatics Toolbox
CLC Combined Workbench by CLC Bio
EMBOSS by UK Human Genome Mapping Project Resource Centre
FASTA by William A. Pearson, University of Virginia
Gene Construction Kit by Textco BioSoftware
HMMER by Washington University in St. Louis Department of Genetics
iNquiry by the BioTeam, Inc.
Lasergene by DNASTAR, Inc.
Lucidyx Searcher by Lucidyx, LLC
MacVector by MacVector, Inc.
NCBI Toolkit by National Center for Biotechnology Information
Peaks by Bioinformatics Solutions, Inc.
Phred/Phrap/Consed by Phil Green, Brent Ewing and David Gordon
Prospect Pro by Bioinformatics Solutions, Inc.
Sequencher by Gene Codes Corporation
WU-BLAST (Washington University BLAST) by the Washington University School of Medicine
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ADF by Scientific Computing and Modeling
Amber, Assisted Model Building with Energy Refinement
ChemDraw Ultra by CambridgeSoft Corporation
CCP4 Program Suite by UK Science and Engineering Research Council
Gaussian 03M by Gaussian, Inc.
GROMACS by GROMACS
JChem Base by ChemAxon, rch
Marvin by ChemAxon
Molecular Operating Environment by Chemical Computing Group
NAMD by NAMD
O by Alwyn Jones
PyMOL Molecular Graphics System by DeLano Scientific
Rocs by OpenEye Scientific Software
SPARTAN02 for Macintosh by Wavefunction, Inc.
SYBYL by Tripos International
VIDA by OpenEye Scientific Software
etc etc
Many of these are NOT exclusive to linux/OS X however some are such as macvector