Re-using D-76

[Xia_Ke]

Jurgen brings up some very good points. Personally though, I don't think this...

...Undiluted developer, warm developer with short development times and over agitation will increase your film's contrast blowing out the highlights, compressing your film's tonal range and leaving what mid tones you have as grainy as a sand storm in Iraq...

... is necessarily a bad thing. It all depends on your desired outcome. If you can spare the film, experiment a bit. For most situations I will do about 5 seconds agitation every 30 seconds for the normal development time. If the lighting is flat, or I just want more contrast, I may do 10 seconds agitation every 30 seconds and develop a little longer than normal time.

[another view]

... is necessarily a bad thing. It all depends on your desired outcome. If you can spare the film, experiment a bit.

Very true - this is the beauty of the world of B&W film processing. I'd also recommend not using D-76, especially when starting out (not saying that I'm much beyond this level myself). Fresh developer is a constant, and re-using it is (or can be) a variable. Eliminate the variables and consistency comes down to process. You can't really be sure what's happening with more than one variable thrown in at one time. D-76, especially at 1:1 dilution, is inexpensive enough. I always pitch it after using it.