My phone has taken to doing this recently - I am slightly puzzled why, since there was no obvious cause. I did update a couple of applications recently, but it sounds strange that this would cause Kies to start launching itself.
My specific problems with the phone are:
1. I have a pattern-based password configured on the lock-screen. When the phone has dimmed the screen and I return to use it, the lock-screen appears, I enter my pattern and then it goes straight into Kies - there is usually a message indicating something about no PC being connected (I don't have the exact text) and then I see the Kies screen (not Kies Air) and it does a media scan of the SD card.
I do sometimes connect via the USB cable, but not that often and not for several weeks. I charge the phone nightly using the standard Samsung charger (see details below too)
2. The phone also, since last night, started popping in and out of Power Saving Mode and it was beeping each time it did (this has not stopped and I may have details of this slightly inaccurately recorded, since I was awoken by it and a little disoriented! I'll re-post if I subsequently find I'm way off the mark).
The other issue that came up this morning was that I tried restarting the phone but there was no change in symptoms (it was still doing either 1 or 2 repeatedly at odd times but not continuously). Then I removed hte battery, waited five minutes and put it back - this was a little concerning, since I then found it wouldn't turn back on and the message on screen appeared to indicate it was trying to charge (despite not being plugged in) and that alternated every few seconds with what appears to be a screen indicating Battery Overheating (I'm not entirely positive - the icons aren't very intuitive but it had a thermometer and an exclamation point). I removed the battery for a further ten+ minutes and then when I returned it, the phone came back on and seems to have been fine thus far.
Other background info is that I've noticed recently several cases whereby the phone has somehow come to life in my pocket and is stuck on the lock-screen. This is a bit odd because my case makes it unlikely the on button would be accidentally pressed whilst in the pocket.
My other thoughts are that, like some other posters have said, something may be up with the USB connector. I'm careful plugging it in, but they are very fine and perhaps it is somehow shorting, tricking the phone into thinking it's being charged or firing up the Kies software. In addition, I wondered if perhaps it could be some battery related issue (just a guess, but it was being charged last night when it went particularly haywire).
If this recurs, I will probably have to take it back to the O2 shop, but for now I'm clear.
Technical details of my phone:
Unrooted
Firmware was updated to the latest 02 version about five or six weeks ago
Model number: GT-I9100
Android version: 2.3.3
Kernel version: 2.6.35.7-I9100XWKF3-CL276555 root@DELL101 #2
Build number: GINGERBREAD.XWKF3
The phone is about three months old and was bought new from 02.