From my experience with low-rent versions of both:1. A radial arm saw is for cross-cuts. It's very difficult to rip with due to a limited capacity and the inherent instability of the cantilevered cross arm making it prone to jams and kickback.
2. The ability of cheap radial arm saws to make good grooves, dadoes, etc...is limited by cross arm sag - you need a *very* high quality saw to get consistent depth across the entire width of the cut.
3. Table saw are made to rip. There's no doubt you can do anything on a table saw, but cross cutting an 8 foot 1X12 in half still ain't easy like it is on a radial arm saw. That's why there ain't no table saws at your local big-box pretend lumber yard for in-house use, only panel saws and radial arm saws.
4. Table saws are inherently superior to radial arm saws when it comes to stability - no cross arm flopping around. With a table saw it's easy to get consistent-depth dadoes and grooves.
5. I had only a radial arm saw for about 15 years. I dreaded using it every time I had to rip something and often thought up alternatives just to avoid using it. I made as many cross cuts on my 10" mitre saw as possible too.
6. I've had the DeWalt portable table saw for about 5 years now and haven't fired up the radial arm but one time since I got the DeWalt. The DeWalt has just an amazingly accurate, stable fence. Like Bill M. says, if you're used to taking 3 minutes on each cut to measure the fore and aft distance from the blade to the fence for every cut you'll think you've died and gone to heaven with the DeWalt at only $500. My only possible regret is not buying the equivalent Bosch saw. The Bosch soft-start motor is a nice feature - I think it probably leads to steadier nerves at the end of the day.