I just replaced my iMac's (glass fronted, 2008) internal hard disk. One thing about Macs, for sure, is that they are not designed for users to fiddle around inside them. And I have not got the most delicate of fingers for anything other than playing the guitar -and sometimes not even that, if I don't do my homework.
In any case, it only took one hour and a half -(including Valium breaks, no, not really) to turn the insignificant* 250GB drive into a spacious (for now) 2TB one. And there weren't too many extra screws when I put it all together again.
* Insignificant? My first hard disk cost me several hundred quid and was a massive 20 MB -megabytes, not gigabytes. And I was never going to fill it up.