Pipetting damage to cells
This is an excellent question, I have been training people to culture cells for about 12 years and students have a hard time grasping this and appreciating the importance etc.

What cells are usually experiencing during pipetting is analogous to a crowd of people trying to fit through the doorway of a building. Shearing during pipetting  is certainly a legitimate concern in cell culture. You will notice its negative effect on viability most explicitly when pipetting cells in freezing
 medium (containing DMSO) following a thaw. Until their DMSO concentration drops their membranes are weaker &amp; more fluid. That's why you pipette the frozen cells drop-wise to the fresh medium, to be especially gentle at this point.

Prokaryotic cells such as the above mentioned TOP10 cells are treated with Calcium chloride and glycerol which has essentially the same effect on their walls and membranes. Hence pipetting should be delicately performed after thawing these cells as well. 

With that being said, if you compare the sensitivity of prokaryotic and eukaryotic cells to shearing, eukaryotic cells are profoundly more sensitive.

For individuals using competent bacteria for sub-cloning and other routine uses, killing a small percentage of of your cells is not that important. However if you are using the transformation to generate cDNA libraries it's very important that you have a titer sufficiently representing the transcriptome the library is composed of. 

In these instances using a more premium competent cell, adhering to correct temperatures and minimizing pipetting is essential. This is why many are taught to swirl the DNA the with the competent cells, rather than the harsher alternative: pipetting up-and-down.

The four most important factors that contribute to cellular shearing are, and in order form most to least contributory:


Diameter of the bore in the pipette tip, the smaller the more shearing. 
Speed at which the suspension is passing through the opening of the tip. The faster the more damaging.  
Size and rigidity of the cell. Larger cells are more prone to damage.  Cells with a murein wall are less prone to damage.  
Concentration of cells. Cultures that are more concentrated are more prone to damage.


Because the make up if the cell itself is so influential on the amount of damage, and because of the enormous variety of cells; designing a representative experiment to assess damage would be very difficult and  laborious.

Finally,  the variety of tips and seriologicals is also enormous. However if one were to attempt to assess this it could be done:

Choose a representative variety of cell lines, choose a representative variety of pipettes. One would probably want to use a robotic pipette to be able to  evaluate incrementally assigned speeds and pressures. Look at different culture concentrations,  phases of the growth curve, time between pipetting and analysis, distance between the exiting fluid and the culture etc, etc.

I think a very successful analysis method would be using propidium iodide and FACS.

After your experiment which will cost a lot of time and $, I think you will find common sense rules: keep pipetting to a minimum and use wider tips whenever possible.