Yesterday I started to try to configure my desktop and my notebook to talk to each other via wireless using the AdHoc mode. The results were far from good - the best I could get, after few hours of desperate hacking around, was a working link with 100 Kbit/s.
The best thing was that my desktop started behaving erratically - almost all programs started to have strange 2 minute hangs all the time. Strace showed that they tried to connect to the portmapper. Disabling, enabling or even removing the portmapper didn't help. After much head bumping I traced the culpit back to a SNAT statement that I put up to allow my notebook to get some Internet - I appeared to SNAT all localhost connections and they had to timeout instead of getting an instant 'Connection refused'.