When you consider most i7's are around the 3.4Ghz stock speed, and most can overclock them comfortably to 4.2Ghz+ you are getting a notable performance increase for nothing.
The only thing you need to OC to that level is a after market cooler for the CPU, again, these aren't too hard to fit and there is a lot of information around explaining it.
There are many options for coolers, "air" coolers are large and some cases wont fit them e.g -
http://www.overclockers.co.uk/showproduct.php?prodid=HS-011-NC&groupid=701&catid=57&subcat=1395
(note that is a high end cooler)
There are also pre-made water cooling options such as
http://www.overclockers.co.uk/showproduct.php?prodid=HS-003-CS&groupid=701&catid=57&subcat=1395
These use water to cool the system and offer roughly the same cooling as high end air coolers but are much smaller and slightly more expensive.
Lastly, there are full water cooling system which you set up yourself - considering you are asking if overclocking is worth it, this probably isn't for you as they are a lot harder to set up.
Once you have a good cooling system set up, you can then overclock your CPU - again, there are many guides on how to do this and as long as you are careful you won't come across any problems!
The thing to note is not all hardware can be overclocked, many suppliers such as dell "lock" the bios preventing you from overclocking.
Hope that helps