Have not had a chance to use it on Mac yet, but I detest it on Windows.
It works just fine when only a few tabs are open.
However, as soon as it gets to 15-20 tabs, the browser becomes unresponsive. Firefox has no problems whatsoever under the same usage scenario.
I also hate it how this program ignores all the IU conventions. For instance, on XP it looks like a Vista/7 application... Which, obviously, costs resources.
I am not holding my breath for the Mac version.
Safari is not perfect, but it is really the best browser for OS X.
Never had any problems with a large number of tabs in Chrome, not in Windows or OSX.
As for it looking like a Vista/7 app..it shouldn't require any more resources since a custom user interface is needed anyway (Windows afaik doesn't have any built-in support for tabs). XP is so damn ugly that anything that doesn't use its interface style typically looks better. On Win7/Vista it fits into the user interface style really well. It also fits OSX quite nicely, but by comparison looks bland with the gray theme OSX has.