Partial cell subculture? - (Apr/21/2010 )

I have a general question. I've recently noticed that some of my fellow labmates have been:

1. Leaving cells in tissue culture flasks without passage for well over a week.
2. Passing cells and leaving them in the same tissue culture flask.
3. Do a partial subculture, for example, they passed cells in a flask and put them into 2 T-175 flasks at the next passage number; however, they left some cells at the initial passage number and continue to let them grow.

All of these things seem completely wrong and go against what I learned about cell culture techniques for the past 5-6 years, but I wanted to know if anyone knew if these are viable methods?

Well, they are all bad techniques, and potentially altering the results they are getting by changing how the cells behave (lab evolution).

My comments:
For "3" in your post lifting the cells, taking some out and leaving some in the old flask is still technically passaging the cells, as you have diluted out the original stock. Essentially this is the same as "2" in your post.
For "1" - if the cells are slow growing or have been seeded at low density it is OK not to split them for over a week. It is good practice to change the medium every few days though, so as to provide fresh nutrients and remove cell debris.

Great thanks. I was concerned.