I've been using the Park patches and they work great. Two of the tubes I've patched developed slow leaks that I ended up tossing, but the leak didn't seem to come from the patch itself. Another tube I ran with two or three patches on it no problem for a few months; still has air in it.
I never use patches on the road (although I carry them just in case I run out of tubes!); I always carry two tubes to use to fix flats, then patch the punctured tubes when I get home and swap them back in the tire, that way I always have fresh and brand new tubes in my bag.