My $0.99
Merging
I've always felt Dev 101 was something best merged with the App dev forum. It seems much less active and unfortunately a lot of new users dont make use of it, nor do many experienced devs venture there to answer questions.
I think we'd see a lot more activity in total if they were merged because I think a lot of devs dont reply to questions in the main forum that they dont know the answer to.
Ultimately I think a dev could come to the forum, post their question, see a "beginner" question and hopefully answer that. Hence we get participation from both angles. As it is now we get some vague questions, complicated questions, and a few good ones.
Moving App and ROM dev
The other suggestion I would put forward is that App dev, and ROM dev, belong next to Theming. Both sections get a lot more traffic than say the classifieds section, and both sections are related to Theming. Theme questions are another thing we get accidentally in app dev. We also see a lot of app dev questions end up in the general Applications section which leads to some confusing responses.
Anyways, there are of course larger concerns regarding traffic to the device sections and space for things at the top of the site. So, in an ideal world App/ROM/Theme dev would all be together up there, but I know Phases has more to consider than just what the organization is.
Prefixes and Tags
I could go either way here. I've never used prefixes much, but if you look on Stack-Overflow the tagging system is excellent. Perhaps rather than prefixes, we could have the tags display under the post title, (maybe next to the user's name). And, ideally, clicking a tag would search the current forum for questions with that tag. I don't know how hard this would be to implement.
With regards to prefixes, my only advice would be to keep them few, short, and simple.
Anyways, those are my thoughts, hope they help
Btw, kudos to Unforgiven and jon for setting this in motion!