Is it possible to extrude a curve/surface along another curve? Right now, I only find the Pipe component. Is it possible to extrude a rectangle or any other shape along a path?
Well you can try sweep, there's been plenty of great models produced with that.
But by the same token, many users have also found it problematic if trying to get specific orientations etc.
Although not restricted to structure (you can define your own libraries of profile shapes that represent anything), I've added tools to parametrically sweep profiles in accordance with typical structural steel modelling programs. There is a library with common profiles for regional steel mills (and I'm happy to add any profiles missing or for timber etc), and you can update the profile table and recalculate the grasshopper definition and it will update. I posted a screen capture using the 2012 stadium as an example, you can see it here. http://www.grasshopper3d.com/video/100222-2012-stadium
If it's of interest, don't hesitate to get in touch.
It's a rhino plug-in, but I've started integrating many commands across to Grasshopper components. You can check out the blog, http://geometrygym.blogspot.com which has lots of youTube screen captures and example files to test the tools with.
Feel free to get in touch if you want to learn more or get some advice as to how it may help.