I can see how it's easy to think at first glance that asking for money is fine. After all, why not save people the bother of buying something, and if people are going to spend money anyway, might as well spend it on what is wanted.
However, keep in mind that there is not a 1:1 correlation between money spent on a gift and the monetary value of the gift. Not everyone goes out and spends $20 on a $20 present right before the party.
Some people stockpile presents (taking advantage of major sales) and shop out of their stockpile. Some people are fantastic bargain hunters and can pay 50 cents for an item that is brand new and worth $25 at a yard sale. Some people might have been given gift certificates to certain stores, and instead of spending it on themselves, they prefer to spend it on picking out a gift for someone else. Some people may work at certain stores or have relatives who do so and are able to get deep discounts. Some people are crafty or creative and make their own gifts.
Asking for money takes away the opportunity for people to do all that. It takes away the chance of someone to give a gift that is worth $25....that they actually only paid $5 for. Requesting WHAT a gift should be takes away the chance for people to be creative/smart with their money and give a great gift for little money.
When someone gives a gift, the recipient has no way of knowing how much that person actually spent on that gift. With money, everything is transparent. It is immediately obvious who spent $5 and who spent $25. Maybe YOU don't care, but many people do. It's not considerate of those who have little money, to take away their opportunity to give a great gift thats worth a lot, while spending very little or nothing out of pocket.
Now, if someone asks for ideas, I think it's fine to say she is saving up for a netbook. But, only if they ask, since that means they likely don't have something else already in mind.