Maximum number of point features in an OpenLayers vector layer

I don't have a definitive answer for you but you I put together a page where you can play around with different numbers of points on an OL map: http://derekswingley.com/lab/olpts/

If the display goes slow because of the too high feature number, it means that the data to display are not suitable for the zoom level. Usually, when the features density goes too high, the display can not be readable anymore (see this example). Even if there was no processing limit and all the display devices were able to display 1000000000000 features in 0.001s on a small screen, the visualisation would remain impossible.

The Töpfer's radix law states that feature density should remain under a constant threshold whatever the zoom level. A way to solve this issue and adapt the data to the visualisation scale is to transform it using generalisation operations like this one or this other one.

I don't think it is not possible to give solid answer for this question. Rendering point/polygons fully depend on browser and hardware (CPU & memory) not with OpenLayers. I had problem with Openlayers and IE6 for one of the Lake (Polygon) rendering. but, it loaded nicely in Firefox. And best option would be monitor the memory and CPU usage with Chrome or some tools would be better.