In solo mining, chances are that the difficulty will increase faster than your GPU can increase the odds of solving a block. Statistically, it would already take years to find a block and collect just 25 BTC (and by that time the reward may be halved again to just 12.5). But right now, you can join a pool and still get some fractions of a bitcoin over time, and get some profit. It costs me $2.70 to run my GPU for a week and collect 0.05 BTC, or ~$10 at today's rates.