I loved Starship Troopers. The movie was OK (didin't do the book justice), but the animated series was pretty damn good (too bad theys topped releasing the CDs), and the soundtrack was excellent (hey, it was by Basil Poulidouris!).
Heinlein's main point in Starship Troopers was basically the evils of war, and fighting, the side you don't tend to see (especially given the recent one). Not some hotshot pilot, or heroic soldier, but on the nasty act that is war. Basically a political book, but then again, most of Heinlein's works were of a political nature. I read them today with facination, because most of the issues he confronted are still around, many years later.
Of course, if you want a real military sci-fi book, John Steakley has Armor, which is pretty damn good on many levels.
As for the Troopers connection to WC, I think it was best summed up in the caption on the back kof the DVD box. That's about it, really.