Like Slovio, Lojban, and Ido, Interlingua is one of many auxlangs like Esperanto. Interestingly though, it seems to be drawing some casual attention based on the methods of it's development, keeping with the Standard Average European model (though I thought 'Common European' would be a much better name for that phrase). Unlike Esperanto and Ido, whose communications are mostly by themselves or with eachother (I've heard that some Esperantists can understand Idists and vice versa), the interlingua.com site claims the following:
"Millions understand Interlingua "at first sight". Speakers of Romance languages especially understand Interlingua immediately and almost effortlessly."

Apparently based on European surveys (mostly across the romance speakers) this language is immediately understandable to many speakers. So, my question is, has anyone used this or had success with this language speaking to a non-'interlinguist'? Or with a romance speaker (e.g. Italian, French, Spanish)?

While there are definitely more reports on Interlingua's success with non-Interlingua speakers (especially on Wikipedia) than there are for Slovio, I'm interested on what you all have to say.

I'll put a clipping of text from the language underneath. And also, I don't think Interlingua will be useful for most eastern languages, I think it is strictly a 'European' auxlang.

Clipping (from Wikipedia article):
Interlingua se ha distachate ab le movimento pro le disveloppamento e le introduction de un lingua universal pro tote le humanitate. Si o non on crede que un lingua pro tote le humanitate es possibile, si o non on crede que interlingua va devenir un tal lingua es totalmente indifferente ab le puncto de vista de interlingua mesme. Le sol facto que importa (ab le puncto de vista de interlingua mesme) es que interlingua, gratias a su ambition de reflecter le homogeneitate cultural e ergo linguistic del occidente, es capace de render servicios tangibile a iste precise momento del historia del mundo. Il es per su contributiones actual e non per le promissas de su adherentes que interlingua vole esser judicate.

Interlingua has detached itself from the movement for the development and introduction of a universal language for all humanity. Whether or not one believes that a language for all humanity is possible, whether or not one believes that Interlingua will become such a language is totally irrelevant from the point of view of Interlingua itself. The only fact that matters (from the point of view of Interlingua itself) is that Interlingua, thanks to its ambition of reflecting the cultural and thus linguistic homogeneity of the West, is capable of rendering tangible services at this precise moment in the history of the world. It is by its present contributions and not by the promises of its adherents that Interlingua wishes to be judged.

(From an essay by Alexander Gode)

Website:
http://www.interlingua.com/interlingua-en

Interlingua can be read very easily by speakers of Romance languages.

However (and this is a big however), I I have heard that it isn't as easy to learn as Esperanto. Therefore, it is easy to read a text someone else has written, but it is not that easy to learn to write your own Interlingua text.

Having said this, a speaker of Italian can already understand a great deal of a Spanish or French text. Portuguese less so, and Romanian, even less. But if you speak one Romance language, it usually isn't that hard to figure out the gist of a text written in another Romance language, even without Interlingua.

Yeah I was thinking along the same lines. However I know that Interlingua would be more understandable to the general populace than any one romance language (especially Romanian - beautiful language though ), but I did not realise it was harder. I guess for the natural feel of interlingua they need to make it difficult to learn. I wonder how much speakers of Germanic languages understand?

EDIT: I guess in terms of learning ability, this is where Ido makes a good compromise between neutrality and difficulty.