I agree Belinda, the current housing stock in the US has far too few properties that are well set up for aging in place or living with a disability. We beleive given the current agining of the population that homes with these sorts of modifications, if well done, will actually increase in value. ADA guidelines are a great place to start, but they often don't apply to residential settings--and often the best solution for an individual does not conform to ADA specs. For example, a walk-in bathtub won't meet ADA guidelines but can be a great alternative to a traditional baths. And barrier free shower options are offered by companies like Best Bath http://www.best-bath.com/ or can be custom built and you'll have a bathroom that looks beautiful and upscale, not like a public facility.
About a year ago I posted a short primer on bath retrofit options on my blog--it's a good overview of options and has a picture of a nice wet-floor shower we did--rather unique in that it provided access from two seperate bathrooms, increasing the flexibility for the homeowner. If you work with someone who is experienced in this area you can creatively solve design issues. Options are increasing all the time--one company now makes an insert for tub cuts that makes it a walk-in tub, preserving use of the tub for able bodied folk. Something I wasn't aware of a year ago.
http://iyhusa.blogspot.com/2007/02/options-for-more-accessible-showering.html