Hi shirtguy!
Regarding the bug with some of the video placeholders, I’ve been able to identify and fix the issue. I just released SlimFast 1.0.1 for that purpose. Can you upgrade and let me know?
The thumbnail was served by YouTube’s ssdefault format. Unlike what its name let us think, this format doesn’t exist for all videos. We’re now using the hqformat, which is much more reliable. This format is a smaller (480px vs 640 px width), which makes images even lighter. I’ve reduced the default video size to 560px to avoid bluriness.
A big thank you for flagging this issue went under the radar of v1.0.
Now about your greatest wish… I had considered pros and cons about offering to create local copies of thumbnails instead of serving them directly from YouTube. I’ve seen it on the Lazy Load for Videos plugin. If thumbnails are on your server, you are basically free to cache them as you wish. I did some tests to evaluate the added value and balance it with the extra code it would require and decided not to go that path, at least for now!
Happy to get other suggestions in this box. I might not be able to satisfy them all, but the feedback is always useful to move forward.
ps: what’s your website?