Following Servant's example/idea, let me describe a bit some of my development cycle/activities/needs, and my opinion if/how GDNet could help. Give or take a bit, most or all of mobile game developers I know follow a very similar path.
- Idea generation/gathering: not helped very much by sites or forums. GDNet could help on this a bit, probably through the forum itself, but not much.
- Programming: I'm helped mostly by Google (which 90% of the time drives me to SO) and sometimes IRC. I dont think GDNet would help me much (but I could help newer people and people who like to post more than I do, I rarely post), but eventually I could ask some more tricky or ambiguous problems which are hard to Google.
- Game art - initial phase: I usually do some basic drawings myself, and grab free icons from iconfinder/iconarchive just to get the concept done. Sometimes I some images from opengameart. When I need a photo I usually get the water-marked version from a photo-selling site (so I can purchase it later if I end up using it). For audio usually opengameart. GDNet could help A LOT on this (when the marketplace has enough content for that).
- Game art - polishment: after the game is getting more ready and I have a clearer picture of which exact images I want, I subcontract with someone. For this I usually talk to a friend (or a friend of a friend). GDNet could help on this (find people with talent, see their portfolios, their "score", price, etc).
- Testing: I usually test the game myself or ask a few friends. GDNet could help on this (volunteers on the forum, and/or via the game showcase thing).
- Showcasing my game: I usually think about making a landing page but end up not doing anything. GDNet could help a lot on this (already will, with the showcase)
- Support/Feedback for clients: I offer an email for support only, sometimes a Facebook group/page. Having a small forum would be great for this. GDNet could help on this (already will, with the showcase)
- Monetization: I usually discuss and read a lot about it on some forums or sometimes Googling, and discuss a bit also. Values paid by ad companies change every day, new companies are formed, strategies change (2 years ago selling your app was the rule, now ads are the rule), etc, so a forum is the best place (due to its ever-changing dynamic nature). GDNet could help a lot also (forum itself).