Precedence, and grounds
"considers that general international law does not contain any prohibition on declarations of independence. Accordingly, it concludes that [Kosovo's] declaration of independence on the 17th of February 2008 did not violate general international law."
Not a single prohibition? I'm not familiar with general international law, so I don't know. This is interesting, however, because it means anybody with a de facto claim to territory can declare independence. As far as I know, Abkhazia, for example, is de facto independent. I can't wait to see what the UN says if and when Abkhazia and similar proto-nations present their case, though I privately suspect that they won't get the same treatment.
There is, of course, a qualitative difference between Kosovo and Chechnya (for example) on the one hand, and Transnitria, Abkhazia and South Ossetia (for example) on the other - but given the article's quote, the International Court of Justice recognizes no restrictions to declarations of independence, and thus does not seem to distinguish between them legally at all. Of course, international recognition is another issue, and anyway I doubt Kosovo would decide to peacefully go back to Serbia had the ruling been made otherwise. I fear that when another breakaway nation presents its case to the ICJ, some law may indeed be found to rule the declaration illegal, and doing so could seriously undermine the credibility of the instution; so either the ICJ really is impartial, or they've made a big mistake (unless there are some legal technicalities not mentionned in this article). Either way, I am curious to see what repurcussions the ruling will have.