I bought two hardy cyclamen tubers in April and planted them as soon as I got home. They have yet to show anything. Is it possible I planted them upside down?

It's possible that they were planted upside down-it's kind of hard to tell which way is up. You should dig them up and see what's going on. Cyclamen are definitely worth growing if you can find the right location for them (shady, with rich, well-drained soil). Once established they are very hardy and quite lovely in spring when they bloom.