Thats been my experience - I bought Powerex 2300mah NiMh based on their winning a camera industry AA battery shootout a few years back. I was using a digital cam and a few diff flash units and these got a work out, normally I was recharging some of them daily. They started fading after 3yrs of steady use. All charging and conditioning was done with a Maha WizardOne Charger Analyzer.

When they 1st started showing some sign of fading, I bought their latest, the 2700mah Powerexs and they've been a disappointment. They never showed more than 2350ish type numbers and after a year or so of use, they've already begun to fade, showing decreased capacity and increased self discharge.

I use LSDs where I have to use AAs now.