The profiles are stored at:
C:\Users\<username>\AppData\Roaming\Slic3r\

But the Slic3r it self doesnt require any installation.

Q1 :
Is it possible to re-use old config-files?

Q2 :
Is it possible to have two installations of Slic3r

New features
ability to fill small gaps using multiple automatic extrusion widths

Maybe this will fix that problem with hollow walls.  I had this trouble tying to make standoffs for my new electronics

This is nice, sometimes I need a lot of solids on top, but don't want to spend an eternity of the base

I was thinking of putting in this request myself.  I run bridges faster to stretch the filament, but on layers subject to slowdown cooling, it would run the bridges slow too, causing the thread to droop.

This would make support easier to remove, but I've had a lot of support that was useless for printing on top of.  Hopefully that has improved as well.

Yay!  This has been the biggest PITA with the .9 releases.

I hope this is true.  Circles have really sucked in the .9 Slic3rs, and I've been using Skeinforge more lately when I want a top quality surface.  I prefer Slic3r for its flexibility.  Skeinforge doesn't support fan cooling, Slic3r can run it for small layers and bridges.  Slic3r can run different speeds and extrusion widths for different kinds of threads, etc.  However it has been more likely to leave seams on surfaces, and blobs that mess up the dimensions and fit of holes.   If the path quality and support generation are up to par, I would be happy to stick with Slic3r exclusively again.

Copy&Paste:

New features

• ability to fill small gaps using multiple automatic extrusion widths

• object information is displayed when double-clicking on an item in the plater

• independently set number of top/bottom solid layers

• descriptive textual feedback for cooling settings

• allow [print_center_X] and [print_center_Y] syntax for all coordinates settings (including bed_center etc.) and [temperature_0], [temperature_1] etc. for all index-based settings

• new min_skirt_length option to ensure that the specified amount of filament is always consumed while extruding skirt

• (experimental) make a little move inwards by 30° before leaving the last perimeter loops

Improvements

• dual-extruder printing was tested and heavily improved

• if brim overlaps with skirt, make brim around skirt too instead of just skipping skirt on bottom layer

• paths are much smoother, without any artifacts

• useless extra perimeters were generated sometimes

• speed improvements

• make external perimeter first on bottom layer when brim is enabled

• distribute skirt loops among all extruders

• remember last used filaments when using multiple extruders too

• use a faster XML parser for AMF if available

• don't apply slowdown factor to bridges

• make a slightly thinner interface layer at the top of support material (nophead's idea)

• expose perimeter/infill/support material extrusion widths in G-code comments

Changes

• bottom layer infill is not taken into account for combination

• use G92 to apply Z offset

Bugfixes

• tool number written in multi-extruder G-code were wrong

• the Split button didn't work anymore

• first layer extrusion width was ignored for skirt and sometimes for other parts too

• the copies number was not updated when decreasing parts in the plater

• honeycomb infill was overlapping too much with perimeters

• the plater was merging all materials into a single-material print

• worked around a wxWidgets issue causing the last changed setting in the GUI to be ignored when saving the preset

• bed temperature wasn't being set after the first layer when first layer bed temperature was set to zero

• fixed regression causing one perimeter to be generated even when perimeters were set to 0

• fixed regression causing too much clipping at the endpoints of loops

Download here!