Well, generalmandible asked for this, but I'm posting this here for the benefit of everybody:
A. The forums has lot of posts with people swooning and praising their favourite desktop shell.

So a search will show up alternatives. But most of those (except for litestep) are paid utilities.
And just a word of opinion - *NEVER* go for DesktopX (stardock) - its a massive memory-eater.
B.Now, as for the question of whether its worth using those to replace the explorer shell, the answer is not a straight-forward one. It goes like this:
1) If you don't keep using windows explorer all day to browse through your file-system, then its worth.
2) If you don't browse web-pages using IE (or a derivative like maxthon/Avant), then its worth.
3) If you don't like the way windows looks, then its worth.
4) If you want more control over the interface (example: you don't want employees to access the "Run" dialog) then its worth.
But what can make the entire purpose of using these shell-replacements redundant, is some people's tendency to browse thru their file-system (folders/files) all day. Now, what I mean is, by using those shells, you have wanted to throw away explorer.exe - but if you run MyComputer or WindowsExplorer or IE, you are effectively bringing it back and loading it into memory. Therefore making no memory-savings. Instead, if you have a complete alternative plan:
1. Desktop shell like aston/talisman/desktopX/litestep.
2. Browser like opera/firefox (whatever except IE).
3. File manager like PowerDesk/TotalCommander/DirectoryOpus/xplorer2.
That is when you see the full effect and power.
But then, you notice that the combined memory usage of using 3 utilities in place of 1 explorer.exe takes up more space on memory usage - you can bring down mem-usage by putting in place appropriate policies. Last of all, consider one thing - many of the utils I suggest above are paid utils (if its good enough to replace, its paid

) - so that is a problem too. But still, its needed for some organizations (or PC-beauty enthusiuasts

).