I used it years ago in a windows app and found it slow, clunky and unreliable - none of what you want in a web app.
Depending what you want to do you may find it better to create a csv file or invest in a com excel template - remember it is the users computer which will open Excel and OLE will simply be used to create the file and save it.
If you still want to use OLE just stick it in a normal source procedure and call it from your Web App like you would in a windows app. You just need to save it and serve it up at the end.