That's quite a hefty gain. I expect it will keep increasing, with more and more people downloading G Toolbar. I don't even remember the last time I actually visited Google, but I use it for all my searches.
I've been getting some suprising SE hits lately as well, such as of course A9 and Dogpile especially.
I'm actually surprised that it's only 48%. I thought it would have been much more than that, based on the percentage of traffic I get from Google compared to other SEs ....
According to this, the market share for google seems to be much higher and yahoo's much lower. Although I don't know where the data is coming from, it seems more likely to me, especially looking at my search engine referral statistics: Links from an Internet Search Engine - Google 93 - Yahoo 4 - AltaVista 2 - Netscape 2