Searching is good when you search for your friend that didn't tell you his UIN/ICQ# or for searching new friends that meet your requirements.
In base mode, you can search using UIN, e-mail, nickname, name and surname. In advanced mode you can fill much many another details.
Be aware that lot of users don't fill all information about themselves. If you search for your friend which name is John, he cannot be found if he leaves his name empty. Nickname can be changed, some people do change their nick often.
other networks Edit
In other networks, search is nearly the same as in ICQ network.
You only don't have the same amount of search parameters.