This past Friday I upgraded our 5.1 VMSA to the latest 5.5 using the standard process (deploy OVF, exchange keys, etc). Everything seemed fine aside from a timeout issue on login that I resolved (vCenter 5.5 Web Client Login - Authenticating hangs for minutes...).
What I am finding somewhat randomly, though, are that lots of operations via the Web Client seem to just start and never complete. You'll get a Starting Task message that sits at 0% and never goes anywhere. Further browsing into the system will then seem to stall in other areas as well forcing a full reload in the browser to get going again. It's almost like the web client's session has somehow become disconnected, but there's no overt error or notice to that effect. I've run into cases where clicking on a certain element that should generate a listing will just go out to lunch. For instance, the vCenter Server Extensions section has a moving progress bar labeled "Objects" but never produces results.
I was, for instance, trying to add a disk to a VM this morning and every attempt just ended up giving me a "starting task" that went nowhere upon committing the operation. To check the state, I logged in with the usual vSphere client and there was no record of my task actually starting. I ended up having to use the apparently-no-longer-being-updated Windows vSphere client to finish the task.
This is a far larger problem for usability than the other issue many are also reporting: control-key combinations via any webkit-based browser on OS X don't work in the remote console. That makes this pretty useless, especially for Linux-based VMs. (No ctrl character passthrough in the Web Client )
Anyone seeing similar behavior or have any suggestions? I've seen this from both Chrome and Safari on OS X thus far.