This is the same kind of question as: Is the DROID better than the iPhone? Is it an iPhone killer? The DROID does DROID well and the iPhone does iPhone well. In the same way, people are asking the question: Is the Snapdragon an OMAP killer?
The OMAP/SGX cpu/gpu has its strong points, particularly with 3-D rendering and texturing; most every graphic push to the screen is some form of rendering or texturing (e.g. cube animations for GDE's home replacement).
The Snapdragon does really well with integers as you would expect given its the Scorpion core's strength. But the biggest boon for Snap is that its REALLY good on batteries. However, if the HD2 is an indication, their battery life is comparable to current OMAP applications. If you want to see longer battery life, you'll have to look at Acer's attempt to make a long lasting smartphone and how they under-clocked the Snap to achieve it.
OMAP is mature and powers the best smartphones and tablets out there. Snap is gaining some momentum, but don't be fooled by clock speeds, because they mean not very much. The short answer? We'll have to see. If you look at the OpenGL bench tests, the iPhone 3Gs running OMAP/SGX running at around 600-ish MHz outperformed the Snapdragon with optimized drivers on the HD2 in just about every test, except integers.
Take it for its worth. To me, this is like Intel vs. AMD back in the day. AMD kept upping the clock, but at the end of the day, Intel was just making a better integration of chip. And that's really what shines about the OMAP/SGX is their integration and how well they work together despite not boasting the clock numbers of the Snap/Imageon combination. At the end of the day, you may not notice it.