In most cases, your computer will page out when you run out of memory. When this happens, your computer will off-load some information in memory to the hard drive. The significance of this is that your computer goes from using one of the fastest components of your computer (memory) to the absolute slowest component (your hard drive). When this happens, you are likely to see the spinning beachball or experiences stutters in your performance.
Page ins are the opposite. It is reading information into memory. This is supposed to happen. For example, when you turn on your computer, the operating system is loaded into memory from the hard drive. These packets show up as page ins. It is impossible to say what number of page outs are bad. You may have 500,000 page outs after 2 weeks or after 2 hours. One may be acceptable and the other is certainly not. A general rule of thumb is to look at the ratio betweeen the page ins and outs. Personally, I don't want any page outs so if I am running on 1GB and I have a 3:1 ratio, I will buy more RAM. But, for most people, if you have less than a 2:1 ratio, you should probably consider getting more RAM.
Also note that your computer "pages out" when you put your computer to sleep. Basically, it writes out the information in memory to the hard drive to save power and then loads it back in when it wakes up. Try this. Check your page outs before putting your computer to sleep and then check them again after waking it up from sleep. So, if you are the type of user who is frequently putting your computer to sleep, your number of page outs is going to be inflated. Don't interpret this to mean that you are short on memory.
A good test to see if you need more RAM would be to do a clean restart of your system thus clearing out the page in/out information and then open up all of the programs that you would typically have open at the same time and do a few tasks with these apps that would constitute normal activity. Now, go and check your page outs. If you have more than a couple thousand, you probably don't have enough RAM.