TWITTER: Ability to edit previous/older tweets (you can’t do that at the moment)
MYSPACE: When editing comments that users have left on your profile, add a ‘Delete/Edit’ selected button at the top of the page! Man, this is a gaff – what if you have hundreds of comments (or even 20?); currently you have to scroll all the way to the very bottom left of the “Edit Comments on Profile” page to find the ‘Delete Selected’ button (bottom left).
Chat – as I mentioned previously on my Twitter page, the fact that they have added the ability to chat with your fellow MySpace friends who are visibly online is a really cool thing, but that chat area at the bottom of the page is too big, and needs to be edited (I don’t know how exactly, but make it less obtrusive visually on the page).
FACEBOOK: They are continually making their site better and better, I’ll probably add a few, but can’t think of any at the moment!
WORDPRESS: Although the auto-save feature for WordPress posts seems to get better and better, a kind of method such as a JavaScript alert pop-up box if an author accidentally hits the back button on their browser before saving the post (which I have done a few times on my laptop!) confirming whether the author really wants to exit the page (with a message like: “You have unsaved changes to your post, are you sure you want to exit this page? OK – Cancel”) would be great.
*PLEASE NOTE: I think all three of these sites are great, and really amazing in their own right, please don’t get me wrong, these are just my personal observations on how they can improve on what are already great sites/products for users! (and provided COMPLETELY FREE to the user I might add! 
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Please let me know your thoughts on this below, or feel free to email me at kevin@kevinpajak.com.