Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
There have been some decent entry-level standard def programs on Linux, such as Kino. If you were masochistic enough to play along with the quirks and straight-jacketed file format limitations of Cinelerra, well, you could spend many happy months trying to get that to work. Sure there are some nice conversion utilities like Avidemux and Handbrake and (for you command line lovers) ffmpeg and mencoder. And high definition? Well, please just forget about it, unless you really like self-torture and inevitable failure and aggavation. Trying to edit 24p HDV in Cinelerra? Been there, done that, and have very little hair left for my trouble.
But Kdenlive is the real deal. Finally.