Adioso strikes me as a company with little social sense. Asking how much I 'value' my girlfriend is just... off. And similarly, the fact their normal site actually _admits_ that it has a confusing interface and asks if you want help understanding it is just the oddest UX design I've ever heard of.
Had to go look at the main site again as this isn't my recollection of it. So yes, there is a small "show search help" link under the main search entry, but I don't see this as an admission of a confusing interface. Feels more like helps there if you need it, but unobtrusive if you don't. I think in the problem domain the Adioso guys are in, this is a fair trade off. Not all first time users would understand the conc…
In the long run to the natural language search is a far better solution for searching for flights.