The site
http://allchains.info/ contains some information about BTC and LTC, including an estimation of the next difficulty.
In recent weeks, we have seen the BTC difficulty go up 20% each time and before that it was about 10% each time. That, in my opinion, would drive miners over to LTC and other alts. Now the next difficulty on LTC may be about a 20% increase, which makes sense if many switched over to it.