Gholamreza Aghazadeh, the head of Iran's nuclear program, said that Iranian scientists had succeeded in enriching uranium to a concentration of 3.5 percent.

There is a lot of scary talk going on today, so I did some digging and I finally found a number: Iran has used centrifuges to enrich Uranium Hexfloride gas to 3.5%. Spinning the gas in centrifuges is the most common technique for enriching uranium and was the appoarch used at Oak Ridge TN in the 1940s to create the first bombs. It is a slow and crude method, as uranium hexfloride is very corrosive and dangerous, and is not really used by the US or western nations anymore.

According to Wikipedia:

-85% enriched is considered "weapons grade" and is the minimum purity of the uranium in the US's arsenal.
-20% will create a usable bomb
-3% to 5% is what a light weight nuclear reactor will use. This is most common reactor and what Iran claims it wants to build.
-While the uranium could be placed in a dirty bomb, this would not be the best use. Since dirty bombs simply spread radioactive material, isotopes like Strontium-90 are more effective than Uranium-235

Update:
According to this history of nuclear weapons the average enrichment of the Little Boy nuclear weapon was 80%

Iran enriched Uranium to 3.5%