maybe someone will run into similar problems, so I want to share the solution I found for myself.
With the upgrade to Lion (or in my case, a new MBP with Lion installed and using the data migration assistant to get the data from my old MBP), a lot of SyncServer error messages appeared in console, like these here:
SyncServer: [0x107116cb0] |DataManager|Warning| Client com.apple.Palm:3265638981 image file path /System/Library/PrivateFrameworks/SyncLegacy.framework/Versions/A/Resources/Pal mBladeConduit.bundle/Contents/Resources/tungsten.tiff does not exist.
SyncServer: [0x107116cb0] |DataManager|Warning| Client com.apple.Palm:3265638981 sync alert tool path /System/Library/PrivateFrameworks/SyncLegacy.framework/Resources/Translator does not exist.
AM SyncServer: [0x107116cb0] |DataManager|Warning| Client com.apple.Palm:3265638981 formatter bundle path /System/Library/PrivateFrameworks/SyncLegacy.framework/Resources/Translator does not exist.
So, I tried to track it down.
It appears that Apple changed from 10.6 to 10.7 quite a bit regarding the Sync services, so that old plugins that used to give no errors in 10.6 show up on console.
The currently active Syncservices are all stored in your own
One can either open this package content and try to delete obsolete SyncServices (directories) by hand.
Or one can use the program "Syncrospector" to do this.
In fact, there were LOTS of old iSync remains (Palm, mobile phones etc.) waiting to be cleared.
Some of them have not been used since 10.4 or 10.5 but still were carried over at every system upgrade or even data migration.
After clearing these old Sync services, all the error messages disappeared.
No problems after that, either.
I can really recommend Syncrospector, which seems to be part of the system 10.7
It seems to be able to do a wealth of other things for Syncing, as well.