I really like Markdown but I've grown tired of a couple of it's problems. Mostly I get annoyed with using underscores for emphasis/italics. Underscores come up in web addresses and in text describing code and computer operations all the time and with Markdown I often find myself having italics where I wouldn't want it. Now it's possible that there are some bugs in the parser but it's also possible that the syntax is correct. I think if I had to make a proposal for a better system would I would use much of Markdown but have the following syntactical additions/changes:
**bold** __underline__ ++ins++ --del-- //italics//