First, I hope they are not doing their queries against a production database!
For regular non developers, try using excel, for these reasons:
1) most generic users might have it on their PC already.
2) drag and link tables. There is a little GUI for simple drag and link tables in there.
3) Support. When they get into trouble, they can e-mail me the file and I can see what they have so far. I'll end up writing views or procedures for them to use.
4) They can use the results data using familiar excel interface and functions, which helps since their SQL ability is so limited.
For developers these GUI tools are extremely limited in what you can do with your queries. I've never found one that can do UNIONs, derived tables, or CTEs. I'm not sure if any can even do OUTER JOINs. For simple tasks, they might be ok, but to switch back and forth all day would be a pain, so I just type them up.