Discount retailers have been one of the best performing sectors in the market during what's been a disappointing 2008 for investors.With that in mind, I was surprised to see that Dollar Tree ( DLTR) was upgraded from neutral to overweight Monday by JPMorgan. The stock closed Wednesday at $35.63, up some 32.5% year-to-date. The analyst cited the company's above-average same-store sales growth trends and solid balance sheet. Even so, Wall Street has a lukewarm attitude toward the stock, with just six Buy ratings compared with six Holds, according to Bloomberg. With that in mind, I'm here to answer readers' questions: Should you buy it? Is it too late to get into the game with Dollar Tree, or can the stock continue to move higher?