I myself preordered a BFL jalapeno and did some calculations.... at the current network hashrate it would theoretically make me 10x the investment in 4 months! BUT the problem is that only BFL (there are other companies) are planning to release 20k chips (4.5 or 7.5GH/s processing power per chip) in the upcoming months... this will increase the hashrate DRAMATICALLY and increase difficulty by atleast 10x the current 25TH/s... it's quite possible to get a rough estimate on the future hashrate presuming everyone uses the devices they buy... as most of the ASIC companies order data can be found on their respective forums.
What do you think about the future BitCoin network hashrate? Place your bets here: http://betsofbitco.in/item?id=1139