I've occasionally heard of folks who were working solo but had projects of enough complexity that OmniPlan was going to be useful, but in the majority of cases, I think it would be overkill for one-person projects.
(The exceptional cases where it was useful were projects where there were a lot of physical resources - tools, chemicals, that sort of thing - that needed to be scheduled fairly tightly.)
Feel free to
grab a copy from our website, of course, and give it a try - it'll run for two weeks in trial mode and we're happy to answer questions as you kick the metaphorical tires.