The regular #1 X-acto with a #11 blade is the most useful cutting tool in our shop. It is particularly well suited for weeding, processing, and installing vinyl graphics. Works OK for cutting light substrate (I prefer a regular box knife for that). Because we buy these in bulk and they are all over the shop, they get used for all kinds of cutting tasks that I'm sure there is a better tool for, but it is often the case that the best tool for the job is the one at hand.
One feature of the #11 that can be over-looked is the round barrel, which allows for finer micro-adjustment with your hand than a flat or "faceted" knife which requires grosser motor controls. This is admittedly at the sacrifice of grip assurance, but this knife is designed for detail work that does not usually require a firm, secure grip.
My second place knife is the Gripster. I keep a few of those around. I like them because they don't roll off the table. But I like the feel of the plain aluminum barrel of the #1 better - I get more feedback from it.
I always say I'm going to put a rubber band around the end of my #1s, but I never do. I usually just lay mine down and let it roll around, or sometimes, if I think about it, I will lay them on the groove in the squeegee. Knife management is a learned skill, and somehow, especially with the #1s, they just appear in my hands when I need them.