I have lag since 1.6.1.
I looked up te cause on minecraft forum and I found this thread: http://www.minecraftforum.net/topic/1873598-lag-with-the-new-launcher-161/
(page 2) it starts with a comment of eyedjellyfish78
I read there that the lag has something to do with the new launcher and with graphics cards.
The problem only seems to occur on laptops.
There also was a fix on there but I couldn't use it because I have intel and not INVIDIA (thats what they said).
Its really annoying (I have like 20fps and I used to have a lot more) and it makes the game unpalyable for me
I have also tried to allocate more ram but that didn't help