I've been married twice and never received an engagement ring. My first husband did give me a 1/3 carat diamond solitare for xmas after we'd been married about 10 years, and it was a mistake. It was an inexpensive (around $300) engagement ring ... and don't think the fact that it was worth less than his video game systems exactly warmed me up, either. The man had a home and good credit, he was perfectly capable of financing a classy piece of jewlery for me.
Second go 'round, by now I've realized I'm not really a diamond type of gal, anyway. Our wedding bands are plain titanium (not expensive and virtually indestructible, I liked the symbolism).
All big, clearly expensive rings say to me is you've got money to throw away. You don't measure love in carats. You take any 10 freshly married women, some without rings, some with tiny rings, some with the Hope diamond, and 50% of them will be divorced in a few years, anyway. Diamonds may be forever but marriage is generally a crap shoot (especially for first time out of the box 20 somethings).