I bought some BTC on Coinbase last night and had it sent to Poloniex. I know the BTC wallet address was accurate. Its still pending 11 hours later and doesn't show up in the Poloniex deposit/withdrawal history. Any clue on how long BTC transactions are taking?
How long it takes depends on the fee you paid but generally with a sufficient fee it should show up on poloniex within an hour.
Are you sure you sent to the correct address? Take a look at your transaction ID and see how many confirmations it has. If your fee was too low its possible to accelerate it with viabtc.