user profile:
I´ve been professionally using inkscape for a couple of years now. And it has become my favourite vector tool.
I´m using inkscape for the following workflows:
Mainly for technical illustration (see Workflow A).
For creating icons and images for touchscreen panel (see Workflow B).
For product photography, creating the cutouts with complex clipping paths (Workflow C).
System: Windows XP
Hardware: Intel(R) Core(TM)2 CPU
6600 @ 2.40GHz
3,25 GB RAM

So far I have been sticking to 0.46. In 0.47 a major bug "combining complex objects to a path" plus problems with my wacom kept me from upgrading it. Since 0.48 is out I was keen for using it´s new path features. But before using any of its new features, I wanted to find out if I can maintain my recent 0.46 inkscape-workflow without loosing comfort and speed.

Here is an overwiew of my test results so far:

Workflow A:
Working with extremly large files (from 2000 to 50.000 single objects per drawing; svg.filsize 3MB or more)
Here I start with an PDF-import originating form 3D Software (SolidWorks).

-PDF-Import works fine (just like 0.46).

-"FILE OPEN" Dialog: it takes longer to open a large svg.file than 0.46.
clicking on "open" button: the "open"-button does not visually respond.
you have to wait until preview is generated. (it takes a few seconds). Only then the open-button responds.

-The actual opening of the svg.file takes about 20-30% longer than 0.46.

-Copying a large object (for example a group containing 3000 objects) and pasting it pack onto canvas:
0.46 operates instantly. 0.48 is significantly slower (it takes 2-3 sec to paste object on canvas).

Workflow B: Creating icons
-0.48 works just as fast and smooth as 0.46.

Workflow C: working with photographs (large files )
Here I use inkscape to create a complex cutout and import the clipping path into gimp for further editing.
Or for example I create a drop shadow on inkscape´s canvas export it as png with same pixel-size as original photograph to combine it with original photo in gimp.
- linking the photo within inkscape´s canvas is significantly slower than 0.46!
- exporting a layer from inkscape is significantly slower than 0.46.

Starting Inkscape:
-0.48 doesnt open as fast as 0.46.

Conclusion: So far I´ll stick to 0.46 because it responds smoother and faster.

Hope this feedback is helpful for inkscape´s committed developers.

PS. What do you think, should I post this "speed-issue" as a bug on https://bugs.launchpad.net/inkscape

PS. What do you think, should I post this "speed-issue" as a bug on https://bugs.launchpad.net/inkscape

There are probably many bugs reported on speed and other performance issues. I think the info you've reported will be very helpful, but you should probably search and investigate what has already been reported. Then if there is something closely related to yours, you can add your info to that bug (if there is one, and I think there might well be).

But no doubt ~suv will be along shortly, and provide comments which will make this very easy for you to do