Poker moves a lot faster online than it does live. In a typical casino with the dealer shuffling by hand you will see about 20 to 25 hands an hour. If they use an automatic shuffler, that can go up to 40 to 45 hands an hour. Online, you probably see 50 hands an hour at a slow table and close to 100 hands an hour at the faster tables.
The speed of the table is determined by how long players take to make a decision. With the various buttons, most players make the majority of their decisions before the action even gets to them. Especially when they plan to fold or just call along. Now add in the fact that many players are sitting at more than one table at a time playing online poker and the number of hands they see in an hour begins to skyrocket. This also means there is a ton of information available about how they play.
Several companies have designed software that that gathers all this information and collates it. The software can cost a bit of money but, it will pay for itself in short order if used correctly. The software is not only gathering information about your opponents, it is also gathering that information about you. This makes it easy for you to spot leaks in your game and then fix them.
The software uses a bunch of numbers about almost every action that takes place in the game. When you raise, how much, what cards you hold when you do, whether you fold or call when someone reraises you and the list goes on and on. In actual practice, there is too much information for you to worry about all of it all the time.
The heads up display can be configured to show you instantly updates information about the players at your table. Pick a few key statistics that will help you get a feel for how you or your opponents are playing and tell the software to only display that information.