All versions of the beta, including the current one, do not zoom smoothly with my mouse wheel. The mouse, a Microsoft Natural Wireless Laser Mouse 6000, scrolls smoothly with the wheel in all other programs.
Also, the map works smoothly for all other functions such a panning and rotation. The zoom is jerky whether in 3d or cloth map mode. Slow rotation of the mouse wheel produces no effect. A rapid spin of the wheel will usually result in a small increment in zoom level.
I tried loading Elemental on my computer at work today and zoom seems to work fine there. I don't really have any idea what this might be related to, so I'm not sure what other information to give you to track this down. Has anyone else had this issue?