After having ranted in my earlier comments (sorry for that :) ) - I revisited the issue and tried to produce a reduced test case (without involving PDF import):
In the attached file, use the pencil tool to draw a straight line between the two T-shaped figures to the left and right of the page using 'Snap to path intersections' (Note: In Inkscape 0.48.2, you need to enable 'Snap to paths' as well, unlike in current development builds).
As soon as the mouse pointer crosses the page border, CPU usage goes up, and Inkscape pauses quite a while until the other snap target outside the opposite page border is detected.
It seems that the clipped area (or the clip-paths themselves) are time-consuming to be considered for path intersections: each of the small rectangles is clipped with a page-size rectangle.
If the page is filled with such clipped rectangles, Inkscape appears to hang indefinitely (I wasn't patient enough to time whether the calculations at some point are done and normal drawing can be resumed).
Tested with Inkscape 0.48+devel r10640 on Mac OS X 10.5.8 (i386)
After having ranted in my earlier comments (sorry for that :) ) - I revisited the issue and tried to produce a reduced test case (without involving PDF import):
In the attached file, use the pencil tool to draw a straight line between the two T-shaped figures to the left and right of the page using 'Snap to path intersections' (Note: In Inkscape 0.48.2, you need to enable 'Snap to paths' as well, unlike in current development builds).
As soon as the mouse pointer crosses the page border, CPU usage goes up, and Inkscape pauses quite a while until the other snap target outside the opposite page border is detected.
It seems that the clipped area (or the clip-paths themselves) are time-consuming to be considered for path intersections: each of the small rectangles is clipped with a page-size rectangle.
If the page is filled with such clipped rectangles, Inkscape appears to hang indefinitely (I wasn't patient enough to time whether the calculations at some point are done and normal drawing can be resumed).
Tested with Inkscape 0.48+devel r10640 on Mac OS X 10.5.8 (i386)