I used Deeper Darkness a fair number of times as a player. The 3.0 version was great for:
A. Casting a week ahead of time and having handy if you ever needed it.
B. Providing cover to make an escape. (Doesn't work with the 3.5 darkness).
C. Eliminating the possibility of ranged combat (doesn't work with 3.5 darkness either).
D. Eliminating the advantage of a flying opponent. (If he can't see you, he can't flyby attack and has to land and fight on your terms).
E. Eliminating the advantages of high dex creatures without uncanny dodge (such as nimblewights).
F. It was also useful if you had Blindfight, summoned devils (or Thoqqua or anything else that Darkness didn't bother), or had True Seeing active.
Needless to say, the 3.5 version of dakness, being good for none of the things 3.0 darkness was good for (in fact, only being useful for illuminating a dark area without having the illumination be visible at a distance ("We can't see." "I could cast Daylight." "But then the villains would see us sneaking up on them." "OK, I'll cast Darkness; that way you can see but there's no bright light source to be visible at a distance") or eliminating the possibility of sneak attacks for everyone) will most likely see no use at all.
niteshade6 said:
Darkness is one of those spells that was almost never used by players, but could sometimes be used by monsters to slaughter opposing parties (well at least until they rules that everburning torches negate it). As a result I'm not too disapointed to see it go. It might be annoying for the occasional player who found a way to get blindsight and planned on using darkness, but other then that most players should be happy.