Bitcoins are probably a great long-term 'investment', but...
1) Many people have good reason to not trust MtGox.
2) Go back to #1, it's a huge problem.
...
When we look at Bitcoin in terms of expected value, the odds are thus astronomical. The only reason Bitcoins don't trade for 100k USD right now is because...
Some of us remember May/June/July 2011, so it's a wise idea to sell some into big rallies, or BETTER yet, spend some BTC and/or help build the economy with useful projects.
It's perfectly possible to do wihtout MtGox in my opinion. Hope the competition keeps growing.