The short answer would be It depends on how much you're willing to spend. Each person asking himself this will get a slightly different answer since Bitcoin Mining profitability depends on many different factors. In order to find out Bitcoin mining profitability for different factors mining profitability calculators were invented.
These calculators take into account the different parameters such as electricity cost, the cost of your hardware and other variables and give you an estimate of your projected profit. Let's make sure you are familiar with the different variables:
Hash Rate: A Hash is the mathematical problem the miner's computer needs to solve. The Hash Rate is the rate at which these problems are being solved. The more miners that join the Bitcoin network, the higher the network Hash Rate is.
bitcoins per Block: Each time a mathematical problem is solved, a constant amount of bitcoins are created. The number of bitcoins generated per block starts at 50 and is halved every 210,000 blocks (about four years). The current number of bitcoins awarded per block is 25.
Bitcoin Difficulty: Since the Bitcoin network is designed to produce a constant amount of bitcoins every 10 minutes, the difficulty of solving the mathematical problems has to increase in order to adjust to the network's Hash Rate increase. Basically this means that the more miners that join, the harder it gets to actually mine bitcoins.
Electricity Rate: Operating a Bitcoin miner consumes a lot of electricity. You'll need to find out your electricity rate in order to calculate profitability. This can usually be found on your monthly electricity bill.
Power consumption: Each miner consumes a different amount of energy. Make sure to find out the exact power consumption of your miner before calculating profitability. This can be found easily with a quick search on the Internet or through this list. Power consumption is measured is Watts.
Time Frame: When calculating if Bitcoin mining is profitable you'll have to define a time frame to relate to. Since the more time you mine, the more bitcoins you'll earn.
Profitability decline per year: Probably the most important and illusive variable of them all. Since no one can actually predict the rate of miners joining the network no one can also predict how difficult it will be to mine in 6 weeks, 6 months or 6 years from now.
Conversion rate: Since no one knows what the BTC/USD exchange rate will be in the future it's hard to predict if Bitcoin mining will be profitable. If you're into mining in order to accumulate bitcoins only then this doesn't need to bother you. But if you are planning to convert these bitcoins in the future to any other currency this factor will have a major impact of course.
If you have a solid business plan, money to invest and access to cheap electriciy, you should consider buying some hi-end equipment.