But what if it affected the job performance? If they didn;t know before they employed you its not the employers fault it is?

Having said this when I applied for a job at a very large British electronics retaiers (the one that sells 555 timers) the interview went very well until I mentioned my co-ordination problem.  I wish I hadn;t mentioned it,

For my current job I was ask at the interview "what was the lowest point of your life". I am not sure if that question was entirely legal but I told them about past problems due to my hearing and another condition (which I told them I didn't want to go into) and in this case I think that actually did me a favour, because the job is all about web accessability.

So I guess it depends what the job is. If you are applying for a position at a rest home, then mentioning you care for somebody at home will be a major plus point, but if you are applying for a traveling sales person posisition then perhaps not.