I came across Interlingua in 2003 and took a basic course that summer and a more advanced conversation course in 2004. It is an easy language to learn if you already speak at least one romance language (French and Spanish in my case). The grammar is simpler and the vocabulary is based on words of Latin and Greek origin that live on in these languages and in English.
I have never studied Italian and couldn't follow it before I studied Interlingua. Afterwards I have been able to understand Italian in films and TV interviews. I used Interlingua for very basic communication on the occasional trip to Italy and the locals understood me. However, Italian has many dialects and (since I did not get any flash of recognition when speaking Interlingua to native speakers of any other languages) my conclusion was that Interlingua can be seen as an artifical dialect of Italian. This is not surprising, as Interlingua is also known as 'the modern Latin'.
After closer inspection of the construction of Interlingua and the bold claims made for it, I don't see a brave new future for it as a truly international language. It is just more fun than learning Latin if you want to see how romance languages hang together.