To be honest, I haven't shelled out the $70 for Quicken for Mac, so I can't answer from first hand experience. My basic online research shows many negative reviews (with virtually no positive ones):
No support for stocks/options
Is unstable on Intel macs
bloated codes, making it bigger and slower than the Windows version
no transaction downloads from banks
constant updates required
questions as to if Intuit will even continue to support Mac
Enough to make me stick with tried and true windows version.
I did buy Quicken for Mac, and made the switch. Here's the real deal (at least as of now -- there were more problems earlier on)
The support for stocks and options is weak
It has been fine on my intel mac
It is native PPC, so has to run in Rosetta which makes it slower than it needs to be (think Microsoft Office 2004 type of experience)
You can download transactions from banks. However, smaller US institutions don't tend to support the mac users and international support is even sparser. Banks, however, often have some kind of basic download support, which you can then import in an extra step or two into QMac
I haven't experienced constant updates (maybe that was earlier on)
Intuit has said they will release a new version, but it will first be a "subset" of the current features. Not likely to be a player.
The look and feel and workflow of QMac is rougher than QWindows. However, you can do a number of changes in preferences which helps control the clutter and confusion (for example, one option -- close current register when opening another -- is a must, or you end up with about 12 windows open at the same time, but is not set as a default on install)
A major issue is that QMac doesn't support migrating your data from QWindows. It really, honestly cannot be done to any pleasing level. I wanted to chuck Windows so bad, I "started over" with my data, but not everyone wants to do that.
Overall, if you deal with major US financial institutions, don't have a lot of stocks and trading, you're willing to wade through relearning the interface and you are OK starting over w/your data, it's a workable solution. If you already need to run Windows (via bootcamp, parallels or VMWare) then just stay with QWindows.