I am suddenly less excited about the arrival of my Cube tomorrow...

Plan to spend some time with it. If yours works out of the box (i.e. no loose screws, good PSU, full speed) then it sounds like you might be one of the lucky few.
I have 2 cubes and can't get 1/2 (15 GHs) of the advertised 30 GHs (for one unit) consistently out of BOTH of them combined. Yet I have all Os in the web GUI.
I've run into bandwidth issues running multiple cubes on the same proxy or router. Try running a second proxy on another machine for the second cube.
Thanks for the suggestion. I have tried multiple setups over the last 3 days and can't seem to get it working right.
Even running 1 proxy with 1 cube on the same switch doesn't yield 15 GHs. Which given the advertised 30GHs shouldn't be too much to expect. I have tried BFGMiner 32 bit (on win7 and linux) as a proxy and I also tried the mining proxy on windows. I also tried a direct connection to mint.bitminter.com (which does have get work enabled).
On the direct connection, I could understand the traffic limits but no on the local proxy. I am on a 1 GB Ethernet switch - even if block erupter only has 10 or 100 MPS the host PC is 1 GB and should be able to saturate both cubes.
I even tried running the mining proxy with an account on slush's pool but no luck.