Yes, about 30% of my overall portfolio is leveraged, currently. That ratio moves around depending on the market, I regularly take profits on my leveraged positions, and then wait for the next correction to leverage up again.
So far, it's working out well for me, my leveraged portfolio has done well enough to wipe out almost all my paper losses in my non-leveraged one.
My leveraged strategy is to only buy stocks that a) pay dividends at a decently higher rate than my borrowing cost, and b) that I am willing to hold for the long term, if necessary. This allows me to sleep easy at night, as even when my leveraged portfolio is down, I know that I am getting 'paid to wait' until the eventual recovery. I'm only buying stocks that are intentionally lower-risk, telecoms, utilities, whole index funds, etc. Even if the market takes years to return, I still have positive cash flow annually on these.
I'm essentially running two concurrent strategies right now, the first is my non-leveraged portfolio, where it's pure couch potato, a mix of low cost index funds held for the long term. I've sold nothing, and made no changes, since the recession began. The second is my leveraged portfolio, discussed above. The latter is just to add value where possible.
Like the poster above, I also intend to pay off some or all of my leveraged portion, depending on how the market goes. I don't want to be stuck buying equities in x years from now with the TSX at 15k.