How Much Is Obama Benefitting From Foreign Campaign Contributions?

Potentially quite a bit:

There’s more money reaching presidential campaign coffers from Americans overseas this election cycle than any previous one but some campaign finance experts warn it may be impossible to ensure no foreigners are donating to the election funds. While both campaigns say they rigorously vet donations, experts say that the large number of donations, particularly those through the Internet, opens the doors for fraud.
“This is obviously a concern,” said Larry Noble, a former FEC general counsel. “There is a limit, frankly, to what they [the campaigns] can do.”
Already, Democratic presidential hopeful Barack Obama has received $2.8 million in money donated from Americans abroad, in U.S. territories or military bases – more than what both President Bush and Sen. John Kerry (D-Mass.) raised combined during the 2004 presidential cycle, according to Federal Election Commission records through June, the most recently available.
John McCain has brought in about $380,000, through the same period, the records show.

This is a concern that has been raised with Obama before. In 2007 alone Obama raked in $31 million in donations from contributions under the threshold for reporting to the FEC.
Which demonstrates a major weakness in US campaign law. Obama, whose donations page allows contributors to select from about 200 or so origin countries, could be raking in millions from non-US citizens in small donations (under $200) that don’t have to be reported to the FEC.
If you were a big-money foreigner who wanted to swing a US election (like, say, George Soros) this would be exactly the loophole you’d exploit.