There have been 2 recent changes to Gmail:
Gmail will show images by default, proxied through Google's servers (and "checked for known viruses or malware"). If there's an exploitable vulnerability that can be embedded in a JPEG image, we'd probably have been screwed a long time ago since any website can also show images without any virus checks being run on them.
The changes probably don't affect open tracking. But you won't be able to see user IP addresses / user agent strings.
Gmail will provide more options with regard to saving attachments. This should also not change anything since 1) old-style "open attachment" will still be available 2) attachments are scanned for viruses anyway. Attachments are parsed (for previews etc) server-side, so a (for example) PDF with malicious scripts won't affect users any more than with the old "trick user into opening a malicious file" method.