I'm going to side with kollatt on this matter. A long load time isn't really detrimental to your work. Photoshop, painter, maya, zbrush, all these programs have a load time; thus I am sure most people have come to expect it to a degree. I can say full heartedly that nothing messes up my mojo than encountering a bottleneck during creation that forces me to wait.
I'd compare it to someone demanding your attention on something similar.
I'd suggest rather than having them load on startup by default, just have it be a toggle-able option. That way you keep your load time for most users, and help those of us with extensive shape library's.
