Marcus,
Sounds great. Depending on what you are looking to do, the customizations can be pretty straight forward for a time tracking screen.
I've seen some good examples, such as users making 5 date boxes and 5 duration boxes, so that they can save 5 time tracking entries for the same person with one click. Another is when certain defaults get put in based on the custom button that is clicked.
Now, onto your question. By auto-complete, I'm thinking that what you would like is that if you had a dropdown list of:
Bob Andrews
Bob Barker
Bob Crider
...and if you typed "Bob" and hit tab on your keyboard then the first Bob would be selected, in this case Bob Andrews. Right now what you need to do is click the down arrow on your keyboard to highlight the first Bob Andrews and then click Tab. So it's a couple extra keystrokes.
I feel your pain. In fact, we've been working on something similar "in the labs" here. I anticipate that the autofill will be available in the next update, likely in the next few days. So stay tuned.
Now, if that isn't what you mean, please elaborate and I can give you some more tricks and tips.
Paul