Frequently with the snapshots my mouse will be trapped in a "drunken" state, where it becomes very laggy and unreactive. It will stick like this for 15-60 seconds, then snap back into working normal only to get drunk again within a minute.
If I press "E", the mouse pointer is very reactive even in the drunken state, it is only the view angle update that is sluggish. Pausing the game doesn't seem to make it go away either, though it's difficult to be sure.
Both the trackpad and my (admittedly wireless) mouse exhibit this problem. Disabling either doesn't fix it.
I've tried to turn on logging on lwjgl, but nothing seems to be coming out of the logs and nothing is noticeable in F3 between when the bug hits and when everything's okay.
This problem happened on 1.6 before, but I upped RAM and things went back to okay. I've tried again (up to 4GB), but to no avail. If I revert to 1.6, things are still fine. This is something specific about the new snapshots.
It is very hard to play Minecraft like this.