NoReason: let me address your points one by one.
I just tried the uploader, selected the thumbnail option and it added the '-150x150' text to the filename. How big was the image you uploaded? I can't say this for sure, but the thumbnail may not be created if your server doesn't have the resources to load a large image.
RSS feeds were at one stage cached in sitemeta, but that got merged out at some stage, I added that code back in 3 weeks ago in the development code. Even better, if you use an object cache it'll use that instead. Grab the file from this page: http://trac.mu.wordpress.org/browser/trunk/wp-includes/rss.php
The code on the download page is a stable release, not a release candidate.
