MJKPHOTO  I just upgraded to TimeLog 4.3.9, having used version 3 under Tiger previously. Unfortunately, the program crashed when I attempted to enter the date of 10/31/2008. TimeLog stops responding. I finally worked around the problem by entering 7/31/2008 and then changing the 7 to a 10. Until this bug is fixed, I can't use the program. I had to go back to my PowerBook to get my billing done.   
(Version 4.3.9)

MJKPHOTO  Make sure you try Billings before you buy. Go through the program thoroughly because it has a very set way of doing things and if that doesn't fit your workflow, you will be terribly disappointed, as I am.

Billings tracks work through the use of projects and work slips that track time spent, (or flat rates, quantity, expenses, or mileage). But if you have multiple projects and different billing rates per client, you have a problem. For one, Billings doesn't seem to allow multiple projects on one invoice, which is very odd. That means you must have one project per client, with multiple work slips. But I have several projects for one client within any given billing period.

Tracking time. Billings has a nice timer feature, but again it is very limiting. There doesn't seem to be an easy way to indicate start and end date/times on invoices, even though you can track that information (but don't expect it to be intuitive or as easy as other reviews have indicated).

While the program does produce good looking invoices, designing your own is a cumbersome process.

Documentation leaves much to be desired. This program is counter to my workflow and has been most frustrating.

Sometimes template driven software is good to have, but not this program... at least not for my business. I wasted my money because I didn't have the time to properly try it out. Don't rely on reviews. Take the time to test it according to your own needs, even if the software is offered at a discounted price.  
(Version 2.5.5)