I just added the title of my posts in my URL, so I changed the permalink. Usually, it's something like aullah.com/?p=123 and now I've changed it to aullah.com/2009/10/sample-post/. However, it is listed in Google for the old permalink will this effect SEO? It does redirect from the old permalink to the new though.
I gather you;re using wordpress? With the newer versions, the wordpress software is supposed to redirect from the older url to the newer one and as you note this is working for you. Google will pick up shortly the redirections and change the urls in it's database to point to the newer ones.
Shouldn't as all traffic (ie search engine, inbound links, etc.) should be redirected by the software. That feature doesn't work on some wordpress installs so I would be sitting on the webserver's error logs to see if you start getting 404 errors. If so you'll have to do some htaccess page redirections to fix them.
nothing will go wrong as theapparatus mentioned, but old url will keep on displaying in the links till google crawls your new url. so be patient nothing will go wrong....!
Yeah it won't effect anything, now if you had a backlink going to a specific page and you changed the url of that page, you will lose that backlink - so if you consider this losing google rank.. then you might be. Otherwise, your good.