That isn't true though. Although memory is finite, unused memory is useless. If the memory were to get close to being too full, the OS kills off inactive apps. I repeat that users should not worry about how much memory is used, it is not a relevant factor in Android performance. Android manages memory in a completely different way to Windows.
Yes, Android manages memory in a completely different way to windows.
Yes, automatic task killers are generally a bad thing.
I repeat that users should not worry about how much memory is used, it is not a relevant factor in Android performance.
No, that's not quite true. It doesn't matter how many times you repeat it.
Let's start by considering that not all memory is created equal.
Go to settings / application manager
You'll notice you can toggle between "cached process" and "services in use".
These are two different and mutually exclusive types of memory. If you look at the bar chart at bottom, there is some more memory not listed....let's call it system. It is a constant. If you add up system plus cached processes plus running services, you get the total memory available which is some fixed number slightly less than 2GB. Since the system portion is fixed, that means the cached processes have to share the remainder with the running services. There is only a fixed amount of memory available for running services plus cached processes.
Running services does include things that are currently in the foreground. It also includes apps that load a "service", which is something higher priority than a process. Look at your services and you'll see things that always stay in memory: widgets (most of them), swype keypad, firewall, 3G watchdog, Tasker, Call Recorders, swipepad etc. Widgets have to stay in memory so they are updated when you switch to your homescreen. Firewall, 3G watchdog, Tasker, Call recorders, swipepad have to stay in memory because they react to other things going on. Swype keypad is chosen to stay in memory because it supports a variety of other processes, so it's assigned as a service to stay in memory. Again, these services are all high priority and tend to stay in memory.
Now look at cached processes. These are apps you've recently run. Having a program in cache will help load it much faster if you launch it again or pick it from "recent apps".
Now let's say you launch a new app that's not in cache... what happens? Somethings got to get flushed because there is only a finite amount of memory allocated for running services plus cached processes. The services don't get flushed because they have to stick around, so a cached process gets flushed (Probably one that hasn't been used frequenctly or recently.) In other words, the services are higher priority than the processes.
Now, let's say someone follows your advice and installs many many programs without regard to memory usage. And let's say many of these load services ... like widgets and other examples above.... and I'd say very likely the call blocker is a service. All of these services are going to carve their space out of the available space, which means less room for cache. Less room for cache means more often you have to grab your programs from storage which slows things down. When cache gets really low you have to go back to storage every time you switch apps (even if you're just going back and forth between two apps) and things get really slow. If you squeeze it even further so there is no cache whatsoever and services have to be flushed in order to run a new program, then things will start not working correctly becaue the things that rely on services assume they are always running.
So, in summary: all memory is NOT created equal. Memory is not infinite. Installing programs which launch services (visible in the service portion of your application manager) reduces memory available for cache and can affect performance, particularly as the cache gets squeezed to a small amount.
I'll admit - 2GB is a lot of memory. If you've got a new phone you haven't installed enough programs to notice it. Most likely no-one will notice the effect of a single call blocker program. But over the life of the phone if you believe performance of the phone is completely unrelated to the programs you install (and whether they have services), you may at some point become unpleasantly surprised.