I've ran 64 bit Ubuntu for the last few years with no issues at all. In fact, Ubuntu Linux is the only 64 bit version of ANY operating system (including XP 64 and Vista 64) I've had that's actually supported all of my hardware.
I do recommend you don't base your opinion of Linux on the opensuse flavor of Linux. I've tried it several times and each time I find myself disliking it more and more. If it works for you, by all means use it. But I didn't have comparable experiences in suse as I did with Ubuntu.
As Mak said, Ubuntu is popular due to how easy it is to use. Yes, it is Linux, so don't expect a start button or the ability to run .exe's, but I find it to be an extremely user friendly distro while still offering high end features to keep most tech-heads happy.
Another +1 for Ubuntu is the forums. They have a huge forum base with a truckload of traffic that comes through. Many posters are actual developers for Ubuntu, so a good chunk of them spend a lot of time daily posting answers and helping users.