Until fairly recently the conventional wisdom was that if family history researchers had a Mac their choice of genealogical software was very limited. The options often seemed limited to Reunion or to try to run software that had been designed for PCs. Recently that situation has been changing. New software has become available and announcements indicate other options will soon join them.
If you are looking for genealogy software, a good place to start is MacGenealogy.org. This site had lots of information about genealogy products for the Mac environment and attempts to be impartial. Don't confuse this site with MacGenealogist.com which should be your second stop.
Much of the Mac genealogical community is on hold while awaiting the appearance of Family Tree Maker for Mac which like its PC version is backed by Ancestry.com. This is not to say that this much awaited software will dominate the Mac market. Its long running PC cousin is an important player but does not dominate that market for serious genealogists. The marketing and distribution power of Ancestry will be important as will links within the program to the Ancestry database. The expected release of Family Tree Maker for Mac currently is the end of November. This will be just in time for it to be a holiday gift.
Family Tree Maker has long enjoyed the best retail distribution system among genealogy software programs. At one time The Genealogy Network now Ancestry bought Family Origins but did not develop or market it. This behavior led some to believe this acquisition was made to remove a competitor from the marketplace. After the end of the non-competition clause of the contract in which Family Origins was sold, its original programming team came back together and wrote RootsMagic. RootsMagic built from a foundation of its Family Origins fan base and has become the program of choice of many serious genealogists.
In the near future it will be interesting to see what happens in the marketplace as Ancestry salts Family Tree Maker with little green leaves that link to content in Ancestry. RootsMagic seems to have aligned itself with the revitalized FamilySearch. After the New FamilySearch opens to non-LDS members in the next several months, RootsMagic will be able to offer similar links to extra content from a powerful partner as well. 2011 should be interesting.