What is SPOJ?
For those who don't know, SPOJ is a website where users solve programming problems via submitted source code. In some instances, nontrivial mathematical knowledge is required to succeed. They have thousands of user-submitted problems. My impression is that SPOJ is intended largely for programming practice.
Why did I add a SPOJ tag?
I originally introduced the spoj tag yesterday motivated by this question:
Given n girls and boys how many ways are there to arrange them such that any two boys have atleast 'k' girls between them.
where the author gave no mention to the fact that it was identical to a SPOJ problem (presumably copy/pasted from the site). Subsequently I added it to other SPOJ-related questions, largely for completeness.
It seemed, at the time, an obvious tag to add since there's a project-euler tag. This tag would have been helpful for me, and it didn't seem to be unhelpful for others.
What information does the SPOJ tag convey?
Judging from the SPOJ forums, they do not seem upset about helpful hints and remarks being available on the internet (in fact, they set up a forum for that purpose). They seem upset, however, if workable source code is available on the internet.
The idea of the tag is to highlight this to those who have encountered SPOJ before (and the tag wiki provides a link for those unfamiliar), and adjust their answers accordingly (if necessary).
Could there be a better tag?
I'm certainly not dead set that the spoj tag should exist. But I feel these questions could use a tag.
Only in a loose sense would SPOJ be regarded as a "contest"; it would be comparable to saying that maths.SE is a "contest" to see who gets the most reputation. Nevertheless, I don't think it's wholly wrong to tag these questions contest-math, since it conveys the idea of where the problem originated.
An online-judge tag might be more appropriate, and this would encompass both spoj and project-euler.