Question: If I am messing around with XCode and trying to learn Objective-C, does it pose any threat to my system if I routinely forget to release objects? What is the real consequence of not releasing objects? If I restart my computer will these memory leaks persist?

I am mostly messing with NSStrings and NSTimers and things like that, nothing serious. I'm just concerned about it messing up my computer.

Is there any way to check if there are unreleased objects? What is one to do if they want to check a bunch of code to see if there are any of these memory leaks?

Answer: 
First of all: all processes run in their own virtual memory, so when you kill the process it's memory is being returned to the system no matter how many leaks are there.

Second. By not releasing the object there is no way to tell the system that an object should be freed and that's why all allocated objects will remain in memory even if they are already unnecessary.

Try to start from something like C and not Objective C, cause it's obvious to me that you have no idea what the pointers, RAM and so on really is.
No, you can't hurt your machine by forgetting to release objects. There's very little that you can do to hurt your machine in software short of deleting system files.

As others have pointed out, all memory used by your program will be reclaimed when the program terminates. If you want to check your program for leaks while it's running, you can monitor it with the Instruments tool that's included with Xcode. I won't try to explain how to use it here -- read the docs and ask if you have trouble.

You can also get some clues that an app is leaking memory by monitoring its memory usage with something like the command line `top` program. If an app's memory usage is constantly increasing as you use it, that's an indication that there may be a leak.