Ok, followup:

i tested with

sudo /etc/init.d/kdm stop
export DISPLAY=:0
X $DISPLAY& thunderbird& kwin&

export DISPLAY=:1
X $DISPLAY& thunderbird& kwin&

export DISPLAY=:0
X $DISPLAY& thunderbird& compiz&

export DISPLAY=:1
X $DISPLAY& thunderbird& compiz&

All four scenarios: drag-and-drop works like a charm. There must be some 
other process/config that is interfering (I'm guessing on the Gtk 
level). I'm at a loss on how to proceed finding the culprit. Can I bore 
you with a process list? I'll list the processess as running in the  
last config shown above ( X $DISPLAY& thunderbird& compiz&) as compiz is 
my default window manager, first:

==[ pstree -u sehe ]================================
gconfd-2

bash---pstree

bash-+-Xorg(root)
     |-compiz-+-compiz.real
     |        `-emerald
     
`-thunderbird---run-mozilla.sh---thunderbird-bin---9*[{thunderbird-bin}]

=============================================

Next: a dump of processess from my 'normal' (kdm) session:

==[ pstree -u sehe ]================================
adept_notifier
artsd
dbus-daemon
dbus-launch
dcopserver
gconfd-2
kded

kdeinit─┬─alltray
        ├─karm
        ├─katapult───aspell
        ├─kblueplugd
        ├─kio_file
        ├─kio_media
        ├─kio_system
        ├─kio_trash
        ├─klauncher
        ├─knetworkmanager───knetworkmanager
        ├─4*[konqueror]
        ├─konsole───bash───pstree
        ├─python
        └─smart-notifier

kdesktop───sh───compiz─┬─compiz.real
                       └─emerald

startkde─┬─kwrapper
         └─ssh-agent

kicker
kio_uiserver
klipper
kmix
knotes
knotify
ksmserver

bash

thunderbird───run-mozilla.sh───thunderbird-bin───9*[{thunderbird-bin}]

=============================================

Is there anything in the list that you don't have running? I could see 
if I could launch that in isolation again to see whether it breaks 
drag-and-drop. Right now the list is a bit too long, and many programs 
probably non-trivail to launch manually :)

Cheers,
Seth

Seth wrote:
> Rimas,
>
> nope I just hovered about a full minute (I'm on the phone waiting :))
> nothing changed. Thanks for confirming that you have it working. Do you 
> mind if I braindump anything special about my machine/config?
>
> Here goes
> - it is KDE 3.5.8
> - Linux sehe-desktop 2.6.22-14-generic #1 SMP Tue Dec 18 08:02:57 UTC 
> 2007 i686 GNU/Linux
> - Thunderbird version 2.0.0.6 (20071022)
>
> also.... (drumroll) I just remembered I have a potentially unusual X 
> config, in that kdmrc contains (among others :))
>
> StaticServers=:0,:1
>
> This simply means, that I don't have to manually launch a second X 
> terminal. I use both terminals on a single display, switching with 
> Ctrl-Alt-F7/F8/F9 etc - no heroics on driver level.
>
> As it happens, :1 is "my" desktop (:0 being my wife's :)). Now it 
> shouldn't, but it might influence the inner workings of drag and drop - 
> being X-based IPC? I know, this is pure guesswork [of the most construed 
> kind], but let me know if something resonates.
>
> Maybe you can see how comparable situations work on your Gutsy box? In 
> the mean time, I'll compare running on :0 to :1, and perhaps running 
> 'just' thunderbird as the sole client to a fresh X/Xnest/Xnvc.
>
> Hope to be back in touch,
> Regards,
> Seth
>
> Rimas Kudelis wrote:
>   
>> Hm, it works as intended for me on Ubuntu 7.10.
>>
>> Seth, perhaps it's just delayed reaction? I get similar problems when
>> dragging music from Rhythmbox to my Desktop, for example. Sometimes you
>> just have to wait a few seconds longer for the cursor to change (that
>> indicates you can now move/copy the item).
>>
>> Note: my experience is with X.org, i've turned off both Xgl and desktop
>> effects. This could be important.
>>
>>
>>     
>
>