I would say that it is worth the money to get a decent G wireless router for home. They are pretty simple to set up, then you don't have to worry about having one machine always on to act as the host computer. If you are using a desktop machine as your host, then chances are you don't have wireless capabilities with it unless you bought one with an on-board wireless, or have already spent the money on a the wireless PCI card. If you only have notebooks, then if the host notebook is gone, or off, your having to hook up the wire because the host is gone....
I see that curcuit city is running a deal on the Linksys WRT54G router for $49.99 which happens to be the exact same price as the PCI card. The router has 4 ports for any machines you want hard wired.http://tinyurl.com/ealcr
The other advantage to having the router may be better security, although I have never set up an ad-hoc network so I am not sure if it is just as securable. The router also acts as a firewall, which is kind of nice, and you have a great deal of control over which ports or open or not. For instance, I have a NAS that acts as a webserver and FTP server, and the router controls the port forwarding and also has automatic DynDNS configuration so that I don't have to worry about the fact that my ISP requires a dynamic DHCP, so I always just have one web address and don't have to worry about a changing IP address.
Way more than you asked for, I know, but it is nice having the flexibility to do what I want and to grow my internal network with existing equipment. It is worth $49, IMHO.