Now we are back on 91.0, how do we linuxites use it?

Click the help tab in weblobby. It contains both link and instructions. Basically: download provided engine manually.

I've lobbied for making this an automated case, so that might get solved even today.

An additional caveat is that you need some dependencies to use static spring, which are usually solved by installing the regular spring package.

The download is only for 64 bit systems. I'm working on a 32 bit static build atm. If you're on 64 bit then yes, install spring from ppa and follow instructions in the help tab and you are safe.

All this hassle is because when 91.0 came out spring devs had not yet started providing static linux builds.

If 91.0 is in ppa you can actually take a shortcut instead of waiting for a static build by creating symlinks to spring executable and libunitsync.so in ~/.weblobby/engine/91.0/.

UPD: I made a static build, no guarantees that it will work. It does for me though. Extract into ~/.spring/weblobby/engine/
http://springweblobby.googlecode.com/files/spring_91.0_portable_linux_i686.zip

It is possible to tell Springlobby to use an alternate unitsync.so (though not really useful).

Apparently, the path you have in your springlobby configuration is bogus.

Will the spring executable run when confronted directly?

Yes. When the spring executable is run it just works like normal.

I think that ikinz has got it working now. The static build he provided plus this unitsync (also by ikinz) got it working for me. It does not work on weblobby however.