I've never had problems with the supposed rapid self-discharge of NiMH cells. And now I have proof.
Almost two years ago, I visited a friend in Gold Bar WA for Christmas. I took some camera equipment, including freshly charged NiMH cells for the flash. I didn't take any flash pictures, so the cells remained unused in the camera case -- which I just got around to unpacking yesterday. (Really.)
Four of the cells were 2700mAh Sanyo AAs. They all measured about 1.23V, rather lower than the 1.4V NiMH cells commonly charge up to, but close to the "nominal" 1.25V of NiMH and nicad cells. Contrary to Urban Legend, they were not completely discharged.
I put them in a Canon 580EX II, and the flash fully charged up in less than two seconds. I fired off some shots. The first few recycled "instantly". The last two took about a half a second. I didn't run down the cells, but it was obvious that two years of sitting on the shelf had no rendered them unusable.
The belief that NiMH cells rapidly self-discharge is utter malarkey. Where it came from, I don't know.