Hi Paul
I'm using Ubuntu here and I use a combination of wxWidgets and Geany, sometimes with wxGlade or XRCed to create GUI's.
Iv not really played with any other toolkits for long - wxWidgets seemed to make the most sense to me when I first looked, so I stuck with it.
I use Geany because it allows a single click to test/run your application, although there is nothing like a debugger involved, and it is quick and clean with a tabbed interface.
I noticed a short discussion about apt/synaptic: I don't see much difference between the two, except of course that synaptic makes a whole lot more sense to anyone who has used Windows for any length of time. Really its just about using what you are comfortable with.
As for databases, I have only used sqlite3 for fairly small scale apps, but it seems robust and is quick and easy to use if you have even a basic idea about SQL statements.
If you have any specific questions (just generalities, I'm no expert!) by all means drop me a line - You have my email address.
regards
Max