Good luck with your project Renton, sounds interesting. I've barely started and my real estate business is residential, so I don't have much for you. I have recently gotten good leads of my internet sites so I'd say they are a success, they need lots of improvement.
As far as residential real estate, it's a no-brainer... our National Association says that 70% of homeseekers use the web in their search.
As for business ops...hmmm... the audience for a given business is very narrow and confidentiality is a big issue. I always wonder about advertising them in an MLS, much less on the web.
Although you have to have a real estate license to do it, the two are vastly different professions, you might search around for a community that specializes in selling businesses for better input.
Gary