I have been riding my Lynskey Pro29 with a Reba RL 100mm fork. It seems that I am constantly bottoming out my fork. (As in the rubberband on the fork tube is always at the top of the fork.

Is this a sign that I need a longer travel fork?

Using all your travel is not necessarily a bad thing, but if you're bottoming the fork out too frequently, you might solve the problem by increasing the air pressure (and therefore the spring rate) in the fork. Could be it's not set up right for your weight.

You should be bottoming your fork occasionally. If you're bottoming out hard or all the time, that's an indication you would be better suited with a stiffer spring.

+1

^ What he said and he "+1".

If I went mountain biking and didn't bottom out the fork, I'd think something was wrong. I use all the travel regardless of how much there is - if the bike has more suspension, I go faster and hit things harder. That's what it's there for.