What should be problematic in uploding 300 Images or more in one step.
The control do it Image by Image. Maybee HTMl has prolem with that. But in Silverlight you can Design uploading with much more Options. Take a look into an FTP Client . This Functions are the reference for massive Uploads. We have build for our Software thus functions with Silverlight.
And we also build in Dynamic chunksize . To give best User Experience. But most WebDevleopers think they are the Standard. And offer us limited User Experience.