Most of the Hosting Company would not show you how much Memory Usage is limited on your Windows Shared Hosting Account.Worst, they just shared all the memory together.

Although memory pool will automatically refresh, but that is a very bad thing for a DNN that is in Shared Server. Most of the time your website just hang there and all of your works either not being load / Save or crashing the database's data. I personally encounter few times that require me to access to database directly to delete the last entry in order to view back the particular page. Did I forgot to mention some server provider won't let you access to database if you do not have static IP? even so, it comes with lots of red tapes.

I once Installed DNN on a shared hosting that limit the memory usage on 64MB. Guess what? It can't support 20 peoples simultanously on the website. Updating website etc takes so long, eventually...the server provider has suspended my account due to frequently memory overload. The beauty is, I just using modules that comes with DNN, and using page cache only, not memory cache.

Later, I installed DNN 4.8 on a semi-D with 512MB. Then Only the website starting to fly. My best record is getting 250 plus people online together, so far so good.

back to the topic, what will the minumum Memory requirement for DNN 5.0?

Based on my past experience, its minimum requirement to run a smooth mini website is 128MB, for micro / testing, 64MB.
For production / Business Website, 256MB is a must. Which, making DNN like fancy CMS among all.

BUT, I still like DNN, after having heart breaking experence with Joomla, Mambo and Drupal. Vote for DNN Now!