Nearly all my SharePoint 2013 development are done on my trusty Lenovo Thinkpad T410S which has a Core I5 (first gen) and is thus limited to 8gb ram but has a sweet SSD which helps a lot since everything is using the disk simulatenously.
For development purpose, it's a all in one server (domain controller, SQL Server, SharePoint Farm) running Windows Server 2008 R2 (I find it less resource hungry than it's 2012 brother for the same end result, same goes for SQL Server 2008 R2).
Like all SharePoint environment, relevant tweaks are mandatory to ensure smooth performance.
- Make sure that you just activate the minimal features & components on your server & apply relevant tweaks (eg : disable disk indexing, disable last file access timestamp, disable logging on IIS, ...)
- Make sure that you install only required components in SQL Server 2008 R2 (core services & management studio are enough for all my needs). Since I work with snapshot, I put my databases on recovery model simple. That also helps to minimize disk access without penality. 2008 R2 works smoothly with SP2013. I've yet to find a customer that will upgrade both Windows Server & SQL Server 2012 just for SP2013 - right now 20130130 -), Pre growth all your content database (mainly the temp one)
- Make sure that you turn off all the services that you're not using (eg: access, excel, document conversion, translation service, etc.) my SharePoint vm do have only the minimal required services and that really helps. Also turn off / minimize the logging, minimize the search performance - Set-SPEnterpriseSearchService -PerformanceLevel Reduced - (and no need to have everything in real time for dev purpose so watch out for your crawl schedules)
I've had the chance to deploy a SharePoint 2013 farm in production which is composed of two servers (each with 16gb ram), one for SQL Server and the other one for SharePoint 2013 (WFE + App server thus). So far everything is ok, will start doing load testing in the coming days but so far so good. I wouldn't suggest to go for less since the cost of ram (even on cloud hosted VPS) will be much cheaper than a slow system.
At work, I do have 16gb on my workstation. I don't see major improvement vs my 8gb setup (but once again, I turn off everything I can). It's handy to simulate SharePoint 2010 farm (client, WFEx2, APP, SQL, DC) but hardly doable in SP2013 right now.
Overall, it depends on what you'll / want to achieve with your SharePoint 2013 setup. Both on development and production. Do you focus on a specific area ? Will you work heavily with search and the new functionalities like content catalog ? Will you do load / stress testing on that environment ?
The 24gb "all in one environment" is obviously when you have everything running with little or not configuration / tweak. In which case the amount of ram will not be insane but for us developers / architect who know what they are doing, I think it's better to implement something working OK with the minimal amount of ram and then that will benefit from beefed-up production environments than the opposite.
To keep things short, it's NOT the unreachable beast hardware wise. Take some time to learn what's going underneath, optimize each layer and you'll get a working environment with the pleasure of knowing where it can be slow and why.
Edit : also know the target system. I'm currently working on both SharePoint 2013 Enterprise and SharePoint 2013 standard. The later having quite a lot less than the former, it's relevant to deploy your (virtual) environments matching the target production systems.