BohnStudios

This is what works for me... Anything that is working on a client's project is billable....whether it's coding, designing, looking for icons, acquiring stock imagery, etc. If you are doing work for someone, you should get paid for it, unless they didn't agree to pay you to do some work that was not in the project specifications. It's important to write clear contracts. COMMUNICATION with your client(s) is really important so there are no bad surprises - for you or them.
 
That being said, I usually try to "hard-bid" projects for new customers because they have not worked with me before and it's reasonable to assume that they want to know what their costs are going to be for their budget. I still keep track of the time and I set a limit for my time...once again keeping communication clear/open always helps.
 
After I do one or two "hard-bid" projects for a client, I usually switch them over to straight hourly billing. I can do this because by this point in time, they have usually been able to see the ROI on the work that I have done for them and there is a certain level of trust established...therefore they value my time and are happy to pay for it.