Here's the deal:
I have 4 computers at home, running windows and MacOSX. I have 1 at work running Windows. Many of these dual boot and run Linux. Two of them have VMs running guest OSes. All of them have multiple browsers; some combination of IE, Firefox, Chrome, and Safari. I use all of them, not because I'm crazy but because the "best" browser changes every 6 months. XMarks managed to keep my bookmarks synced across all these browsers and all these OSes. And it did it painlessly.
I'm not sure why everyone thinks I should "man" up and write my own. I didn't write my own browser, OS, GUI, etc. A fool makes new tools when existing ones are already on the workbench.