My grandparents had a bucket of Loc Blocs; I enjoyed playing with them when I was at their house. One day, when I was in my teens, they were gone! My dad said he took them to Goodwill because he didn't think anyone played with them anymore.
I've become a bit obsessed, actually: if anyone finds a bucket of Loc Blocs with some non-Loc Bloc toys in it as well (probably in southeastern Wisconsin), please send me a PM. Thank you (and yes, I realize the odds are not great)!
Hmm.... All this time, and I only just now discovered this thread.
As described in my article: http://www.retrojunk.com/content/article/10656/index/ I remember loc blocs fondly. Unfortunately, I never had any big sets, just the little $1 or whatever car sets. The main difference between loc blocs (also known as brix blox) and lego is that loc blocs had taller pegs, and taller "plates" (although the "bricks" were the same height. The difference there is that a lego brick was 3 lego plates tall, whereas the loc bloc bricks were 2 loc bloc plates tall). Also, as someone else mentioned, they had a sort of double bar running down the middle of the underside, instead of lego's peg/tube things.
Loc blocs were actually -nearly- compatible with legos. You could fit a lego brick on top of a loc bloc piece (but you'd never get them apart again), and loc bloc pieces would fit on top of lego ones (but they wouldn't really lock together).
Loc blocs are still being produced today, although not under the same name. They are still being produced by the original manufacturer in japan, kawada, under the name "diablock", and they are used in the disney "u build it" line of toys.
*WARNING: The above post may be highly opinionated, read at your own risk.