I have just "downgraded" one more time to the 7.5.2 firmware to see if I can eliminate the popups. I am expecting to still see the disconnect popup initially after the Mac wakes from sleep - but not after copying significant amounts of data to the Time Capsule.
What I have observed after all of this troubleshooting is that when the Mac wakes from sleep on Lion (10.7.2) the network connections are not immediately re-established - resulting in Safari thinking it is not connected to the internet (whether via ethernet or wireless). This could very well be the cause of the post-sleep wakeup disconnect popup for shares mounted in finder. The Applecare tech did indicate that the delay in reestablishing network connections in Lion is a known issue that is supposed to be fixed in 10.7.3. In Snow Leopard (any version) the network connections are reestablished immediately upon login after wake from sleep - or the desktop appearing is delayed after successful login until network connections are re-established (just a guess).
I am going to test whether it will make a difference if a wait a few seconds after waking the Mac from sleep - but before completing the login process - to see if the delay between wake and login allows network connections to be established - before anything that is actually checking for loss of network connections actually runs. On my Macs - I have it set so that user/password must be entered after resuming from sleep or screensaver. I will also test whether disabling the password requirement upon resume from wake or screensaver makes any difference as well.
Also - I thought I would point out here that once you install Airport Utility 6.0 (an update that should now be appearing) - you will be presented with the graphical Airport Utility that is nearly identical to the Airport Utility app for the iPhone and iPad. A number of features of the previous airport utility will no longer be available - and you may find this to be a bit frustrating. Some of the features you will no longer see are: (don't despair while reading this long list - there is a solution for it at the end).
1) No ability to specify NTP time settings.
2) No ability to control whether the LED flashes or stays solid.
3) No ability to specify or update the location information for your Airport device.
4) No ability to view the log or change any logging settings.
5) No ability to view or set IPV6 settings.
6) No ability to specify SNMP settings.
7) No ability to manage profiles.
8) No ability to see or manage the older 802.11g Airport devices.
9) No ability to use the "Add Wireless Clients without a password" (the function that turns the status light blue).
10) No longer any tab for USB printers (printers can still be attached to the USB port and will work).
11) No option to disconnect all users for Time Capsules.
12) No option to archive the Time Capsule disk to USB drive.
13) No ability to view the Airport device status on one screen - you must click around and hover over the various icons in the graphical view to get specific information about each airport device and wireless clients.
14) No ability to allow/disallow ethernet clients when airport (express) device is used to provide wireless connectivity to an ethernet wired device. This functionality will work by default - there are just no settings for it.
15) No ability to allow/disallow a wifi network to be extended.
16) To upload prior version of firmware - you have to hover over the currently displayed firmware version and hold down the "option" key to get a list of other firmware versions to upload.
17) To go directly into detailed settings for an airport device - hold down the option key and double-click the device you want to configure.
For the most part - it appears that Apple has removed all of the advanced features of airport utility - probably in an effort to make the configuration process less overwhelming for a basic user - and I can see why they would want to do this. Most of the items in my list are not "necessary" items for the average user.
Now - for those that are upset by the loss of functionality in 6.0 - there is a Lion-specific full-featured version of Airport Utility (version 5.6) that you can download and install alongside version 6.0. Airport Utility version 5.6 is only for Lion - and will provide all the features that were taken away in 6.0. After you download 5.6 - just click on the dmg file to install version 5.6 and you will have a second Airport Utility icon in the Utilities folder.
The link for the Airport Utility 5.6 is:
http://support.apple.com/kb/DL1482
~Scott