I bought an X5 in 2002 or '03. The only reason I replaced it was due to damage to the touch screen (don't drop your PDA being the lesson learned). I got an x50v as a replacement in 2005. It's still going strong today. Huzzah for WriteShields as I'm still on my first one . I've finally gotten around to buying a GPS receiver for it... just three years later than I thought.
My x50v lasted 2 years before the cradle connector broke inside it. I finished it off by trying to fix it myself. My first x51v didn't last long but they don't like being dropped into water. Fortunately I backed it up daily and replaced it in 2 days via ebay