Currently Google index has 31,300,000 pages hosted on Geocieties.com and in particular, 6000+ pages related to Amateur Radio and 4000+ pages related to the Ham Radio keyword.
This will mean that a large quantity of knowledge and documentation about projects, modifications, antennas and technical tips will be lost.
Yahoo! that owns Geocities since 1999 has decided to shut down the world wide famous free hosting service born in 1995, recommending owners to move web sites elsewhere.
So if you have bookmarked any interesting sites hosted under Geocities, you have still a couple of days to cache them into your PC before they will get lost.