Homebrew PCBs

ANother thought I had about using the photo-resist boards was the 
potential for another problem that I don't know if there is a work 
around or not.

If you expose a board and the exposure doesn't work out as planed, 
it is then ruined isn't it?  

For example, with toner transfer, if it turns out bad, a missing or 
pitted traces or whatever else can go wrong, I wash off the toner 
and do it again and again till it is good enough for what I need.  
The only loss I have is time and paper.

However, from an ignorant point of view ( I have never tried this 
process), if something goes wrong, the board can't be used again in 
the potoresist process can it?  

Also, as I don't know what things look like along the way, can you 
see the traces with the resist on them after developing?  If so, 
what does the developed photoresist look like?

TIA

Chris