Have occasionaly experienced timeouts myself – and as a programmer (including web) I habitually reduce the size of photos before uploading for just this sort of reason. (I should ask now, are you uploading full resolution pics?) In some cases, either the browser, or the server will timeout (get bored…) and in fact, the browser can sometimes choke before the upload has even commenced for real, as it has to scan the entire data file, sometimes numerous times to find some unique strings to use as delimiters before it converts the file to text and begins the upload.
Just this sort of issue has been a support nightmare for me in the past, since users (very reasonably) want it to "just work" without them having to go through any extra steps. But I digress…
Since the site resamples the photo-album pages anyhow, there’s not much point in uploading full-size shots. The whole process will go faster, and I’ve yet to have an upload fail when sending the reduced size since they go so quickly.
I believe this site uses 580 pixels wide for the albums, but I tend to use 800X600 when I reduce images since I also use that for emails and my wife’s facebook posts. 8X6 is just a nice round number that fits on even the oldest displays (these days) without distorting the aspect ratio.