I would be careful about send threads into Twitter and having bots hitting your site in mass numbers too frequently. I did the same at first and had the same issue of the site slowing and giving me 503 time outs. To be honest the MyBB forum I ran coped OK doing this with Twitter, but I have found things are quite different using XenForo. But I'm only on shared hosting and it's not geared up to be doing that type of thing "auto sending forum threads" into Twitter, Facebook and Digg like I was doing before.
I've stopped doing it now, plus it's only spamming them SN services anyway and it usually gets you nowhere.