I recently picked up a useful tidbit from engineering on a Flash Player optimization setting that can be helpful when using the vSphere Web Client or any other Flash web application for that matter. The particular setting is the Website Storage Settings which controls the amount of temporary data that can be stored by the Flash Player on your local disk and by default this is limited to 100Kb. This limited storage footprint is actually done on purposes as a security feature of Flash.
However, at some point the Flash Player will reach this limit and prompt the user to allow additional disk space to be consumed and this is where you may see the vSphere Web Client crash and you would to go through the motions of logging back in.
To avoid this scenario, you can change the default 100Kb to unlimited for a particular site which I was recommended so that I would not hit this problem. I do want to stress that this is not a VMware best practice but more of a general Flash Player best practice but I think it is something to be aware of and could help from a usability perspective.
To check your current settings, Adobe has made it very simple by just navigating to the following URL: http://www.macromedia.com/support/documentation/en/flashplayer/help/settings_manager07.html
A panel will load and you will get access to a variety of Flash Player settings including the Website Storage Settings which is what the link above will default to.
You will now be able to browser to the particular website, in our case we will be looking for either the hostname or IP Address of your vSphere Web Client Server and you will be able to see its current usage as well as limit. To change the default, you just need to click on the website and then move the toggle at the top to the far right which will show up as "unlimited". I would recommend you make this change for all your vSphere Web Client servers that you access. It would have been nice to see our vSphere Web Client automatically detect this and recommend the change or automatically default to this setting.