I have a CETMA rack on my mountain bike and I have been very happy with it. I went with the wide rack, it can do two file boxes, no problem. I don't know what Lane recomends for load capacity, but handling is fine with 30 pounds. The most weight I ever carried was 6 gallon jugs of water (about 50 pounds.) Handling wasn't great with 50 pounds on the front, but I managed just fine getting across town and going up and down some decent hills. You can strap things on much faster than with a back rack, and put a hand on anything that starts to move. Even after a few drunken crashes it is holding up great.
-James