There are no dowloading speed restrictions in 0.25.0, or indeed restrictions of any kind. The search engines no longer work, though.
Some things to try:
* When you start downloading, open the connections panel on the queue tab (hit F9) and see whether all 20 of your threads are connecting OK, and at what speeds. Actually, start with a small number of threads (5-10).
* Check Log tab for error messages.
* Check whether your ISP throttles usenet traffic at peak times or all times. Changing the usenet server port you connect to, or connecting via SSL, may help with this.
* Temporarily disable firewall & antivirus.