To get the count of a query without returning results, simply specify pagesize=0.
http://api.stackoverflow.com/0.9/users?filter=mike&sort=name&pagesize=0
{
"total": 1161,
"page": 1,
"pagesize": 0,
"users": []
}
/search seems to be an exception and likely a bug. see pagesize=0 on /search throwing error