I (English-speaker from the US) took Portuguese classes in graduate school. Everybody in the class but me was a native Spanish speaker and they struggled mightily to get the Portuguese pronunciation right since the two languages are so similar. I had no trouble with it at all since I didn't speak Spanish and the teacher used to call on me all the time to read stuff while castigating everybody else for their bad pronunciation.
Spanish speakers often assume Portuguese will be an easy language to learn because both are very similar in grammar and orthography, but many end up sounding with a heavy spanish accent when they attempt to speak Portuguese because they don't emphasize phonetic differences and proper pronunciation compared to students from other languages do.
It's strange that as a native portuguese speaker, I can understand spanish (at least the mexican one from chavo) fine, but my spanish friends can't understand me at all.
That's pretty normal, a few years ago I ran into these Brazilian bikers in Argentina and they didn't speak Spanish or English, so it was really hard to communicate. We (Spanish speakers) really rely on you guys understanding us. I can read Portuguese without much trouble, though, it's the pronunciation that gets me.