I've got a little over 20gh/s total, not even sure if that is respectable but I've been at it only around 2 weeks now. Anyways, my new blade was hooked up last night, just a few rounds ago it found a block.
You certainly were lucky!
As already mentioned by al.matic, the mean time to generate a block at 20 GH/s is currently over 4 years!
If you are interested in the calculation, the formula is:
mean time (seconds) = difficulty * 2^32 / hashrate (hasrate in in hashes/sec, i.e. 20 x 10^9 for 20GH/s, and current difficulty = 609482679).
Even for a 100 GH/s miner the mean time to generate a block is about 10 months, and at 1 TH/s you could expect an average of around 1 per month.