Legally in most countries one is only allowed to stay for a maximum of 180 days out of every 365 days on a tourist visa -- ie you're only allowed a maximum of 6 months out of every year. As far as I know there are no "180 day visas", there are only 90 day visas, that can be extended once for a total of 180 days. Then technically you are supposed to exit the country and not enter again until another 180 days have passed. In places such as the UK you get a bunch of stamps in your passport specifically stating the dates you entered and if you try and enter again they will turn you away. Although Argentina stamps your passports, so far I've never come across an agent that has enforced this.
After 180 days your country as well as the other country that you have been staying technically can argue your residency status. ie "Snowbirds" -- Canadians that head to Florida for the winter -- know that they've only got a max of 180 days in the States or they may have to pay taxes as well as have problems the next times they head back in. Also in terms of trying to switch to non-resident status for your home country (and thereby save some taxes) the 180 day rule really has a large say in the opposite direction -- ie you cannot stay more than 180 days in your home country if you have non-Resident status, or you'll suffer by way of your taxation.
Argentina in the past has never cared too much about all this. If Argentina operated the way Canadian or American Border Services act there wouldn't be nearly as many foreigners down here. The official rules in Argentina are the same as other countries, it's just that the border agents don't enforce them. However, perhaps these increases in visa fees are signs that that may change -- but really I doubt it -- I think what's happened is that they've finally clued in that it's a good money-making scheme so more than likely they will allow the continued abuse of the 90 day visas as long as people are happy to pay increased penalties.
