edit 15 May 2011
Some feedback from NetApp is that this will work *IF* the SDW and NET3.51 are installed first before putting NET 4 into place.
In our environment, .net v4 also appeared to block installation of BES 5.0.3. My support chain contacted NetApp engineering, who says that .net v4 is supported.
FWIW, we are using Server 2008 R2 SP1, with all updates (straight install), VMware ESX and ESXi v4, UCS hardware. I do not know the NetApp filer model/version.
What we saw: after install of the base O/S, we installed the NetApp v6.3sp2 LUN driver. Everything appeared to work failry well, until we committed to the LUN and the connection process started. All we ever got was the 120 second time out. On the back end, the LUN looked connected at the NetApp, but on the server, there was nothing. Attempts to reconnect at that point resulted in being told that LUN was already dedicated.
Removing .net 4 components from the server allowed full, normal, LUN connection.