I discharge and recharge everytime. I bought a LaCrosse charger and it will tell me which batteries are not getting a full charge. Most are fine but some are not so good. I have about 8 to 10 sets (4) AAs. I have a 4 year old so some go to toys.

I recently bought 4 sets from Ebay and when I went to just charge them (2500 mAh NiMH Energizers) they charged on an average of 1400 mAh per battery. I put them back in for conditioning and although it took several days per set they reach an average above 2500 mAh each. Once they go through the conditioning they just need to be discharged and recharged. I have a few (2-3) that I have taken out of the rotation due to not fully charging and one that seems to have gone dead. Don't forget some of those might have been used in the Light Saber.
Doug mention once that about one in ten will give you troubles with fully charging all the time.