Why doesn't my Samsung Galaxy S communicate via USB?

I discovered today that I cannot connect my PC with Samsung GT-I9000 any more: when I plug in the microUSB cable, nothing happens other than that the phone starts to charge. Earlier I got to see Connect to Kies or something like that.

Things I've tried so far:

-Switcing USB debugging on and off
-Removing battery
-Trying different cable
-Trying reimaging PC to a known good state (where I previously would have found new hardware)

-Trying different computer
-Factory data reset
-Formatting internal SD card
-Entering download mode with mUSB jig (my phone has download and recovery modes disabled otherwise) and reconnecting mUSB cable. Then I saw the "USB Device Not Recognized. One of the USB devices attached to this computer has malfunctioned..." error on Windows (XP).

Is there anything else I could try before sending it to the long journey of Warrantyland?

UPDATE: I tried an app z4root which rooted the phone without the need of usb cable, then I could use Rom Manager to force the phone into Recovery Mode (remember my phone had the 3-button combo disabled). There I deleted-erased-formated everything I could and when I got back to normal mode and tried connecting again, Windows found new hardware and Kies recognized the phone. Just to be sure, I pulled the cable from computer, waited for 2 secs and then reconnected but, alas, nothing happenend again. I reimaged the PC and redid the z4root+Rom Manager+Recovery Mode wipe thing but nothing. Then I tried to reinsert microusb plug into phone under an angle and witnessed a successful connection. Kies offered updating firmare. I did not breathe on the phone and carefully clicked mouse to accept in hope that if this was a software error, new update would fix it. The update went fine but after the phone rebooted and I could confirm the firmware version from About, I still could not connect.

Then I used USB jig which I purchased from eBay to force the phone into download mode and tried to connect it with a PC once again. The PC froze at once (even the mouse cursor did not move). I tried pressing every conceiveable keyboard combination from Enter to Ctrl+Alt+Del and then disconnected the USB cable. As soon as I did that, everything started moving again on the screen. I could reproduce this behaviour for 5 times. On the sixth time, however, Windows found new hardware and started installing drivers but soon after that a balloon popped up saying "USB Device Not Recognized. One of the USB devices attached to this computer has malfunctioned [...]". Then I rebooted the phone and came back to the issue later.

I forced the download mode once again and plugged the USB cable in. Nothing happened. No frozing, no error.

Even though I have tried to wiggle the microusb plug in from every possible angle, it does not seem to have any effect. It just works when it wants to work. Charging works always, though.