This is for example triggered when moving a selection. The lag can get up to half a minute sometimes, where the application looks completely frozen.

Does the drawing contain block references or are there a lot of entities in a small space?

Snap / auto snap should be really fast, as we're limiting the search to a small area with a spatial index.

I guess you are on to something, it sure has to do with blocks:

Its best noticable when zooming in model view and measure tool (i-p) active: as soon as snap starts finding points in a block reference below the mouse pointer, then screen redraw gets considerably less snappy.

I also noticed now a very long delay (feels like 30seconds at least) when zooming quite close, eg on corners with the "ss" tool (the /stretch/ command) active. This only happens on windows (7) though and seems to be not connected to blocks. I report more details as soon I better understand. (The computer this is happening on is unresponsive at times, but not to such an extent.)

possibly related - http://www.ribbonsoft.com/rsforum/viewtopic.php?t=1718