Courtesy of the MS App-V blog, I came across a blog post that directed me to an FAQ that Microsoft has posted on their website with frequently asked questions regarding the process for upgrading App-V Clients and Servers to the 4.5 code that was just released.  The FAQ has some great items that describes the upgrade order as well as what compatibility there are for 4.1/4.2 packages moving to 4.5 clients/servers as well as what happens to the SGCache and User Preferences (usrvol*.pkg).  It's a great read.  The only thing I find a little strange is references to the 4.5 Terminal Server client, which seems to not be in the 4.5 code on MVLS.  Strange...