I own Harrison Mixbus, which is basically Ardour with a Harrison console emulation. I've also used Ardour in Ubuntu Studio 12.04 and while it's a pretty full featured DAW, it's not my favourite. I find it clunky and difficult to navigate. That may just be me, though. I also found the plugins support very buggy and if you use Linux you're limited to LADSPA and other proprietary Linux plugin platforms. However I think it got MIDI support in v.3.0 so maybe it's better now? Looking at the website of the newest version it looks like it's upped it's game a bit.
In any case, if you want to record multitrack audio and mix you can't really beat $1.
Yes I use Ardour (2.8 on a Mac) and I like it a lot. The new (3.5 or something) version is stable on Linux only so I haven't tried it out. They want you to donate a bit so I got mine for 2 dollars, after I tried it a bit I gave 'em 25 because it is really good. Used to work with Cubase but I switched.