I've found that if you charge a day rate and deliver the things you promise, clients will never worry about time. You still need to have the discipline to get things done, but it takes the pressure off making sure you are billable for a certain number of hours.
This! I consider it a professional obligation to yell at people who default to hourly billing. Other good things come from day and week rates besides not having to track time; for instance, it incentivizes you to find faster ways to deliver the same work, and makes it easier for you to negotiate scope/price without taking a rate hit.
Daily billing is definitely the way to go. It is a great way to manage risk for both parties versus fixed-price (potential for abuse from the client's end) or hourly (potential for abuse* from the professional's end). Once you have a good idea of what you can complete in a day you can gather requirements and break them up into days resulting in more accurate scopes to work with.
From my experience it seems everyone is happy (especially if you throw in daily invoicing). It's easy to avoid deadbeat clients this way and you have more consistent cash flow this way. If not consistent then at the very least it is predictable since you can see how far into the future you can book days.
*: The abuse referred to here is for clients to keep requesting changes when they pay fixed-price. They are of the mentality that it is unlimited changes, and it is often difficult to draw the line on what is a billable change with this approach. Hourly can result in a professional delaying things to rack up hours.
