Harrah's has added the 'slot finder' to their Web site, basically the ability to see if your favorite slot machine is in one of their casinos. Still, no cool features like a map to the machines, etc...
You can find the slot finder here:
This leads to the larger point - Las Vegas casino Web sites generally suck. They are all basically brochures on the Web, in various stages of design prowess. Now, the biggies do have access to their slot club balances online and that sort of thing but there are still lots of features they could add, not to mention much more comprehensive looks at the properties themselves.