Does anybody know if they're the same or not? A friend told me the Windows one is rewritten from the ground up and doesn't share the same engine. So if something looks right on Windows Safari that doesn't mean it'll work on a Mac?

I think safari is ugly '-' I wouldn't use it lol, I even use firefox when on a Mac...why? Because you have this super awesome shiny interface on mac, then you open safari and it's this crappy brushed metal effect :P

Firefox ftw :P...and theres lots of bugs in the safari for windows anyways.

Yeah, I agree. Unfortunately the client we're working on this site for uses Safari at home, so even if it's 1% of their users, it's an important one.

Any guess why Safari would ignore <br /> tags?

Because it's stupid again and has bugs, if he's using safari on windows thats why, but if he uses safari on mac I don't know...

I wouldn't attack Safari that much - IE6 and 7 are worse than it. Firefox is probably the most standards compliant browser out there, but Safari comes close. I'm still a Firefox fan at heart though

John, Safari between Mac and Windows have several differences.

First, the safari usually shipped with Mac is Safari 2.
The Safari available for windows is a port of the upcoming Safari 3.

On the functionality ground, this bring some differences (XSLT engine not available on mac except when the developer kit is installed), and some odd bugs that are going to be ironed out in the 3.0 version.
The most annoying one I ran to, is when you set/get attributes on an element with a namespace.

For example, you can do "setAttribute('myNameSpace:test',1)" without any problems, but a simple "getAttribute('myNameSpace')" will always return null thereafter.
You have to use the get/setAttributeNS functions.
There are some problems with events being not correctly propagated too, but I let you look there: http://www.quirksmode.org/js/events_compinfo.html

One that really bothered me some times ago: Safari on mac cannot insert new javascript elements after document load dynamically.

After a bit of digging, I found that the biggest bug was that you cannot dynamically add script tags to the document in Safari and expect them to run. This includes external scripts.

And the last major difference I see is based on the screen rendering. Both version use the OS rendering abilities, and specifically when it comes to font faces, there are a lot of changes between the 2 os.
That means that you could see major differences on the text rendering between the 2.

Holy wow that's a great answer! Thanks!

The shelling out to the OS probably tells me the answer?

From an HTML and CSS rendering point of view, I think the difference lies mostly between Safari 2 and Safari 3, although as tripy mentioned, most Macs still have Safari 2 installed, and Windows has Safari 3. As far as I know, both the Mac and the Windows versions are both based on the same WebKit engine, it's just that it had to be ported over to Windows. I think Safari 3 was a huge step up for WebKit, because many of the bugs I had to deal with in Safari 2 were no longer in Safari 3 for Mac or Win.

One thing about Safari though is that it is extremely picky about invalid or usually HTML and CSS, often stopping rendering instead of ignoring the invalid section or taking the best guess. This is, imho, the incorrect behavior for a web browser, but it may shed some light on why Safari might not handle things like <p />.