I put New Zealand white clover into an empty bed last year--the bed is on a slope, and I forgot to mulch it the winter before, and it had eroded nastily. I chucked seeds out in late April or so, and the clover was established enough by August that I was able to start using it for chop and drop. I only had flowers in there last year, but they grew very well, and soil quality increased amazingly. At the beginning of the summer, water just ran right off the bed and everything in there required constant attention, but by the end of the summer, water vanished into the soil and I watered that bed about half as much as the rest of my annual beds.
In the fall, I ripped out some of the clover and transplanted strawberries into that bed. I use shears to cut the clover down to about three inches tall whenever I think about it, and I occasionally go through and rip out some aggressive runners that might crowd the berry plants. The strawberries in this bed are significantly taller than the ones I transplanted into a bed mulched with wood chips and are producing at the same rate as my third strawberry patch, which has been mulched with compost. The really nice thing about the clover-and-strawberry patch is that even in our last streak of warm weather, I didn't need to water at all.
Obviously not a scientific sort of study, but so far I am pretty pleased with the process. I added some of the NZ white clover to the annual bed where I've got my zucchini, and am eager to see what happens.