Yes, Expect: 100-Continue is used by System.Net.HttpWebRequest in .NET, for example, and all modern web servers recognize it (it's part of the HTTP/1.1 standard).
It is used mainly when a file is uploaded via POST (but can be used with any POST request), so that the client can know if the request can be successful before sending the potentially big data.
A 100-Continue response does not mean the request WILL be successful, it means that the parameters the server already knows are ok (eg: it won't throw a 4xx code, for example), and if the rest is ok as well, then the request will be successful.