I love, love Tumi and their bags are so functional and beautiful without frou frou.
Some of the prices on ebay for Tumi do seem amazingly good but they are probably real bags. I visited a Tumi outlet (at Woodbury Commons in NY) last year for the first time and found some tremendous bargains, which made me realized how those bags could be so well priced on ebay. Tumi has new colors and styles every season.
If you find a bag you like on ebay, post it in the authenticate this thread. Though I don't think there is fake Tumi, yet, you never know!!