You can use a Poisson table to determine how many blocks you can expect to find in a given amount of time. For example, at 1 Gh, the expected value of how long it will take you to find a block is 9 days (Network difficulty is ~800TH and you have 1GH/s, so 800TH/(1GH/s) = 800000 seconds). So in a 27 day period, assuming difficulty does not rise, you can go to the column labelled 3 in the linked table (27 / 9 = 3) and see that, for example, you have a 5% chance of mining 0 blocks, 20% chance of mining 1 block, 42% chance of mining at most 2 blocks, etc. Of course, difficulty is rising quite quickly. I would peg the real expected value to find a block at around 2 or 2.5 weeks. If you can stomach that, solo mining does have a higher expected yield due to reduced latency and, of course, no fees.