A quick clarification about trademarks (long)...
Logos are generally protected by trademark (as opposed to copyright or patent). Each type of intellectual property has its own set of rules and protections, so if we want to be precise, its best not to confuse the three together.
In the United States, trademarks are protected locally under common law, but may also be registered and protected at a federal level under the Lanham Act (15 U.S.C. §§ 1051 - 1127).
As the name implies, trademarks arose as markings that were placed on products so that consumers could identify (and thus remain loyal to) the manufacturer of that item. To this day, trademark law exists to directly serve the public interest by allowing them to identify makers of goods or providers of services. Copyright and patent, on the other hand, have an indirect public interest, in that protecting the interests of the intellectual property holder for a limited time encourages them to innovate. This distinction is important, because it provides the reasoning why copyrights and patents will eventually expire, while an in-use and and adequately defended trademark never will.
What manufacturers and service providers are concerned with are the dillution of their trademarks. Trademark dillution occurs when a trademark (or similar trademark) is used in a way (keep in mind this is a very simplified discussion, not legal advice) that diminishes the value of the trademark to identify the goods and services. The analysis of this will depend a lot on a number of factors. In Polaroid Corp. v. Polarad Electronics Corp., 287 F.2d 492 (1961), the Second District developed a list of 8 factors:
1. The strength of the trademark (Kodak is strong, unique, etc. "Henry's" is not)
2. The degree of similarity between the two marks (Polaroid is very similar to Polarad)
3. The proximity of the products (where/how they are sold)
4. The likelihood that the prior owner will bridge the gap (would the original mark holder have branched out to make/sell the goods and services of the alleged infringer)
5. Risk of actual confusion (would a consumer possibly confuse Polaroid and Polarad's film products (likely), or think that the McDonalds foods is behind "MacDonald's Scottish Importing Company" (not likely))
6. The reciprocal of defendant's good faith in adopting its own mark (did a defendant adopt their own mark in an attempt to benefit from an association with the original mark holder?)
7. The quality of the defendant's product
8. The sophistication of the buyers (similar marks are more tolerated if the market is specialized and buyers are expected to have a sophistocated knowledge of the goods and services they are using, thus making confusion much less of a risk).
While the Polaroid case dealt with what happens when a second person uses a similar trademark, these principles have created a system where a trademark holder must protect the strength of their mark, or risk a loss of protection. The most famous example of this would be "Asprin," which was originally a trademark of the Bayer. Asprin was so successful that people began to use it as a generic to describe a type of medicine rather than the manufacturer. Eventually, the courts ruled that it had become genericized. The biggest at-risk manufacturer today is probably Xerox, which is constantly running ads reminding writers to refer to "Xerox brand copiers" rather than "xerox machines." Their dilligence in trying to protect their trademark will be the centerpiece of any litigation when someone tries to trademark "Zerox," for example).
Bringing this back around to topic...
Jon is right. There are many acceptable uses of a trademark. The primary use is to identify goods and services provided by the trademark holder. Thus, a store selling Coca-Cola brand soft drink, might use the Coca-Cola logo to identify that they are selling that product (but would be liable if they used the logo to identify Pepsi brand soft-drink, for example), provided that there is no risk in people mistaking that the store itself is owned and operated by the Coca-Cola corporation, of course. Likewise, a shop guide publisher, might acceptably use the Ford Motor Corporation logo on it's guide to indicate that the guide describes vehicles manufactured by Ford, but would need to do so in such a way (and with a disclaimer) that would prevent any reasonable consumer from believing that the guide itself was a product of Ford (i.e. ACME Car Guide (big letters) for servicing Ford Brand automobiles 1977-1978 (smaller letters) (Small ford logo in corner for visual reference, with a disclaimer inside saying "Ford is a registered trademark of Ford Motor Corporation. ACME is in no way affiliated with Ford Motor Corporation, and Ford does not sponsor or endorse this product.", etc.)). These examples, of course, assume that the association itself will not tarnish the reputation of the mark holder. For example, Mattel toys might sue and win an injunction should NAMBLA (North American Man-Boy Love Association) wish to advertise that they are selling Mattel toys as a fund raiser (and if it isn't clear, this is purely fictitious, there is NO relationship between the two entities, and Mattel does not endorse or in any other way support NAMBLA).
The overall question of legality ultimately rests on how a logo is being used. The news could use the Viacom logo to identify a story that deals with Viacom stock, for example, but could not use the logo at the beginning of the program to suggest that they are a product of Viacom (unless, of course, they are).
Unlike copyright, which makes illegal the copying of protected media (subject to the defense of fair use), violations of trademark do not arise merely from posessing or copying a trademark or logo, but only from specific instances of use. The big disc of rasterized trademarks is not illegal, however the way that an end-user uses them may be. The disclaimer mentioned in John's post above is there because the seller of the rasterized images is not an agent of the company owning the trademark, and therefore cannot transfer the right to use the trademark.
Always trying to muddy the waters.
-Eric