Diversification

Let me first state that my ira is not diversified. I hold 15 stocks which are mostly tech because that is what I understand. My biggest investment is 37% of my portfolio (ATVI) which I purchased at 13.44 and now sits at 27 and I've done some profit taking on it. That is the largest I ever go with any investment (33%) which means I still need to adjust it a little.

These are my investment sizes.
33% very large
10% large
2%-8% medium (my regular investment amount)

My diversification comes from other 401ks. I have left at least three at other companies and keep them in mutual funds (mostly aggressive). I also own property so investing in this account the way I do is diversified in other ways. You should always diversify, not only across investment types, but with investment houses. I would never put all my money into one brokerage house.