I have done it once or twice long long time ago, and the ride is no more bumpy than with a "real" patch or a new tube, because it's the tire that holds the tube, not the other way around.
However, I have been told that unless you smooth out the edges of the home-made patch, the abrupt edges may cause premature failure of the tube due to abrasion near the edges. A little bit like what happens if you ride with a Mr. Tuffy tire liner that is improperly installed.
In my case, I had no problem with the tube(s) I patched, but it was in the "good old days" when 40 psi in a bike tire was a lot.