This is not exactly a Skritter question, more a general Chinese question.

Is there a general rule for when neutral tones convert to non-neutral tones in compound words?

I see that Skritter and nciku both agree that the 生 in 留学生 is first tone, while the 生 in 学生 is neutral tone. I have also noticed that when a two-word character like 辣子 is part of a longer phrase like 辣子鸡 the neutral tone often changes, but this doesn't seem to be universal because the 膊 in 胳膊 stays neutral in 胳膊肘.

James

P.S. Zhongwen says that 辣子 has two third tones, but nciku says the 子 is neutral. Maybe that's a regional variation?

If I ask some people I get the answer like "when it feels right" or "when it's easier to say" but these don't really cut it for me. I've not heard of any rules and I suspect that if there were they would be at best rules of thumb - you are right that there are many, many regional variants and even some cases where both neutral and non-neutral are acceptable (朋友 springs to mind).

子 is usually neutral but in some words like 电子邮件 it's third tone. I'm watching a TV series right now called 手机 and some of the scenes are in a rural area where they say 中 and 不中 with a second tone 中 in the place of 好 and 不好 - Chinese speakers can pick up this difference pretty quickly but I had to ask my wife if it had a different meaning.

Part of the problem with regional tone variations is that the overall pronunciation for certain tones is different in different places. The village in southeast Wuhan where I live has some wonky ones, particularly 你好, where the 好 is pronounced so quickly that it sounds like a fourth tone.

As for specific examples of tone variation, particularly situational neutral tones versus the character's original tone, my Chinese teachers have often told me that either one is acceptable. It makes sense that was 'standardized' after 5,000 years of regional variations would have some quirks like this, so I wouldn't worry too much about it. If you're still concerned about it, though, make friends with a 普通话老师 at a broadcast/performing arts school and run questions like that by him or her; your typical Joe Somebody man-on-the-street probably won't have the answer to a question like that, but a broadcast 普通话 teacher should have it down to a science.