When it comes to poker software, it also depends on what type you are talking about here.
There are the HUDs(Heads Up Displays) like Poker/Holdem/Tournament Indicators that display current information about your cards and some info about players such as M-Zone and streaks.
Then there are the more important(in my opinion) types of software, which is analysis software, such as PokerTracker or Holdem Manager. These programs take your hand histories and pull all kinds of information out of them about not only the way that you are playing certain
hands, but also your opponents. They also have HUDs that you can use to visualize it on screen during the game. These programs are much more accurate because they don't just use the information from the table that you are currently at, but from everytime that you have played those opponents. These programs help a lot more if you play a lot.
I would say that most of the better players use some form of Poker Analysis tool, just because they can find their weaknesses and strengths of themselves and their opponents, but not all of them do. If you are playing a lower limit game, I wouldn't expect that many of them to be using anything.