Iran reports having thousands of centrifuges spinning away to make fuel for their upcoming power reactors. Others think that Iran has it in mind to make weapons material using those same centrifuges. In fact, Iran could divert just 1% of its centrifuge production and have enough weapons-grade material to make a few bombs per year.The article above provides more technical information on using centrifuges to enrich uranium for various uses. More information can be found at Wikipedia.
...A standard power reactor that generates electricity requires about 20 tons of uranium a year, utilizing uranium with about 4.5% U235 content. A centrifuge facility intended for this civilian use would be spinning thousands of centrifuges to do 106,000 SWUs each year. Diverting a bit of that 4.5% U235 and adding just 1,300 SWUs of additional effort would yield 20 kilograms of 94% U235. If this were to be done on the sly, about 1% of the total centrifuge work would have to be falsely labeled or otherwise disguised. Diligent inspectors might catch this, or they might not. _ThreatMatrix
A large number of western pundits -- oriented more toward appeasement than reality -- have trumpeted the "peaceful Iran" message, based upon an eroneous CIA "threat assessment" from 2007. But that message was either hopelessly naive or intentionally misleading. The chumps in academia, media, and the political sphere who fell for that line have conveniently moved on to other things.
Meanwhile, Iran just keeps on keeping on. SWU after SWU after SWU, the uranium 235 just keeps getting richer. (a SWU is a "separative work unit", or one batch around the centrifuge) With Obama as US president, Iran has nothing to fear from the great Satan.