PAC FEC Filings recently made a $2.9 million dollar ad buy for ads to run during the Republican convention, and you can now see their filing data showing up on the FEC web site. (This is the PAC; not the Voter Fund 527)
Seeing such a large ad buy led me to start poking around further on MoveOn’s filings, and I found one interesting note. The FEC appears to be keeping an eye on you can see a MISCELLANEOUS DOCUMENT which reads:
This submission is in response to the Commission’s letter of August 18, 2004 regarding the committee’s 2004 July Quarterly Report.
Please note that all media expenditures disclosed on Schedule B were not allocable to any federal candidate and were properly reported on Schedule B, Line 21(b).

So it sounds like the FEC questioned some expenditures, perhaps suggesting that they should have been listed as supporting a particular candidate.
If you trace back to MoveOn’s July 2004 Quarterly Report, you can see that the section in question, SCHEDULE B ITEMIZED DISBURSEMENTS Line #: 21B shows a bunch of expenditures for things like Internet access, Health insurance, Political Consulting, and others. I guess MoveOn’s contention is that these expenditures — which seem to represent the bulk of their operating expenses — aren’t directly related to supporting any candidate. But the FEC appears to be questioning that categorization, in particular for “media expenditures.” There are some line items for “media consulting” and “media production” — and then there is one line item for a “media purchase”:
Media Strategies
1580 Lincoln Street
Denver, Colorado 80203
Media Purchase 1147414.00

So that particular item — which looks like a $1.1M ad buy — might be the one that is puzzling the FEC. And there doesn’t seem to be a corresponding detailed filing (like the one for the $2.9M buy above) for this expenditure.
Hard to tell anything definitive, and it is worth noting that it’s unclear whether this level of scrutiny is unique to or if every PAC is getting similar memos. But interesting…