Sequential scans are terribly underrated given today's architectures. If the datum is small and it's like 1000 elements max it's going to be hard to beat a simple scan of an array for speed and memory efficiency.
But trees et al also make a lot of sense as a default. If you need the performance to scale in a roughly linear manner you need to be smart about it. This is what sinks a lot of software, usability wise.
