Hey guys,
  Am new here, and new to mining with Nvidia cards.  I've been following this thread for the past week, finally got my hands on a few of the 750Ti cards last night.  Picked up 3 different brands, but have only had a chance to tinker with the MSI twin frozr (no pcie plug) so far.  I am definitely no expert, and am learning cudaminer as I go, but wanted to share my experience so far:

  I've only run one card at a time so far.  Biostar H81S2 mobo, 4gb ram 750w psu.   and mostly using auto-tune, as I dont understand the blocks and warps yet..
System idle = 42.2W (per killawatt meter)
gpu = +0, mem= +0, load @99% = 114W.  hashrate 268 kh/s T5x19
gpu = +0, mem +300, hashrate 252kh/s (T230x1.  this may have been a bad setting by auto-tune, i'm not sure.  i initally was trying gpu and mem clocks others were reporting, and was getting alot of instant artifacting, or 'rapid scrolling' error. so i left it at that, and moved on to doing the TDP raising bios mod.

  With TDP bios mod:

gpu = +0, mem= +0, hashrate 272khs, T10x24, gpu utilization 75% (?), and system load increased to 124W (from 114W)
gpu = +0, mem= +300, hashrate 291khs, T10x24, system load = 130Watts.

  This last setting was stable for 6+ hrs while I was at work today.  I have tried, briefly, with higher gpu and mem clocks, and highest i've hit was ~322khs. but i need to keep testing for stability, as i was getting errors along the way.  Interestingly, the bios mod has definitely increased power draw, and has allowed near 300khs with a modest +300 mem overclock.  I have seen others on this thread with much higher clocks at this speed.  Christian, are you using a modified bios on your 750 Ti?  I feel there is more there.  Also, after the bios mod, the power % on Precision X drops to 75%.  I dont understand this, or if it may be reporting it incorrectly.
   I'll continue seeing how far i can push this card.  I am concerned about the scalability issues others are having, and will assess this as well, when i have time to add other cards (hopefully tonight).  Will keep you guys posted on my findings.