My guitar had no humidification for the first 5 or 6 years I owned it, and I was not playing it much then. When I started playing it regularly, I started using one of these:

http://cgi.ebay.com/NEW-GUITAR-VIOLI...QQcmdZViewItem


It seemed to help, but I was not super regular, and over time it got worse. Humidity is part of the issue I think, but I think it has set up woes as well.