My method of estimating solo block time is as follows:
Deepbit is currently 5269GH/s and they are finding blocks about every 31 minutes. If you are averaging 1GH/s it will take 5269 times longer for you to find a block (on average) than deepbit.
31min * 5269GH/s @ 1GH/s = 113 days
If you mine with a pool you will always be paying something for the privilege (percent fees or transaction fees), and you also trust the pool operator to not cheat. Because of this, solo mining pays better in the long run. The disadvantage with solo mining is the variability. You might find a block in 1 day, you might never find a block. You take 100% of the reward for your 'luck' and also 100% of the risk.
If you can afford to pay your direct costs and carry the other costs for an extended period of time, I recommend solo mining. For reference I'm paying about $5 for 1GH/s (without optimizing) excluding the depreciation cost of hardware, real estate costs (rent, taxes), etc. You have to be mentally prepared to check your miners daily without seeing any results.
If you need the incoming to cover your operating costs, pool mining removes much of the variation particularly if you use a PPS pool such as Arsbitcoin arsbitcoin.com