I've tested at www.rackspacecloud.com cheapest 64-bit, Debian Linux virtual server with 256 MB of memory (1.5c/hour) with the new Concept Application Server running a real-world medium CRM application generated by GyroGears used by telephony-services reseller, application developed by a friend (a non-programmer). I've managed to squeeze about 75 connection with the server still standing up. I wanted to go for 100, but I had no memory on my desktop to open client connections to the server and I was to lazy to go for the laptop. I believe that it could support 100 simultaneous connections. Keep in mind that the test was made on a 64-bit server with minimum amount of RAM. Using a 64-bit system will cause a significant increase in memory usage (about 20%). I'm sure that on a 32-bit server, 100 CRM instances will easily be supported.
In conclusion, I could say that concept:// application have now no significant disadvantages to http://. Peak memory usage was the last major one, but now it's a clear advantage. Peak-memory-usage for server-side processing is incredibly low due its shared-memory pool.