We have the Asahi poll, an FNN news poll (can't say I've heard of it before) and the Kyodo poll as reported by MTC and Mainichi (Kyodo news forbids linking to their web site without permission so no traffic for them I guess). Remember, these polls ask different questions and choose their sample differently so they're not comparable. Also, The Asahi poll was taken before Kan was elected, so they obviously measure different events. You can however see how the same polls change over time and look for common trends.
First, DPJ. They started out with an unrealistic approval rating of over 70% after the election in September. It was pretty clear they couldn't hold on to that level of course; the question was how low they would sink. Down into disaster, it turned out, with around 20% in the latest polls before Hatoyama left. Now that he and Ozawa are gone (or at least out of sight), they've received a healthy support bounce. They increased about 30% on the news Hatoyama and Ozawa was leaving (Asahi), and about 40% by that news and by the election of Kan. So far so good, though not terribly surprising.
The LDP, remember them? Neither does anybody else it seems. They sunk into the 20% approval rate last year before the election, and they've sloshed around there ever since. That seems to be their floor, their core supporters that will support them come what may. On the other hand, they seem incapable of attracting anybody else no matter what happens with the DPJ.
Why is this? They have never yet taken any lessons from the past four years culminating in their election disaster last September. There's been no analysis or introspection, and no change in party organization, political program or election strategy. A vote for the LDP is a guarantee for exactly the same politics you've come to know over the past few generations. And it's no more tempting to people now than it was last fall. When parties fall on hard times (the British conservatives is a topical example) they only manage to come back by essentially reinventing themselves. The LDP so far seems incapable of doing so - and if last years catastrophic election wasn't enough to shake them up I wonder if there is anything that will.
New Komeito isn't going anywhere. Literally. They have their stable core voting block, but like the LDP they don't seem to be able to break out of that even when the DPJ fails. They may go into coalition with the DPJ after the upper house election; a lot of their program fits better with the DPJ than with the LDP after all. But that would also reinforce a perception of a party that values power over all, and is willing to govern with anyone in order to get it. A coalition may hurt more than help among unaffiliated voters. And while their core voters are reliable, they aren't getting any younger.
The Japanese Communist Party and the Social Democrats do seem to at least not lose support, and may in fact enjoy a bit of a bounce themselves. The SDP got a boost from breaking with the DPJ over the Futenma issue, though it remains to be seen if it's anything more than a transient media exposure blip. They remain vestiges of an earlier political era though, and unless they remake themselves both are probably heading for irrelevancy.
The centrist (or center-left depending on your perspective) Everyone's Party seems to have managed a successful transition from a startup to a full-fledged party. They've lost a bit of support to the DPJ since Kan took power (and they lost a local election to the DPJ just now), but at around 8-10% they're the third largest party around and seems set to stay that way. They're the first successful new party, and as such could represent the spearhead of political realignment in Japan. The recent loss in support just underscores that as a new party they need to build support on their own terms, not just be the anti-incumbents. You can't build a long-term power-base on a negative; people become loyal to you based on what you are for, not what you're against.
By contrast, the new parties that splintered from the LDP this spring, the Stand Up Japan Party1 and New Renaissance Party, have gathered exactly no support at all. The polls that even mention them give them 0%. It's a fair guess that their only supporters at this point really support the party members personally; their loyal home district voters. As vehicles for political ideas, these parties have so far gone nowhere.
Why is that? One reason could be that Everyone's Party was first, and cornered the market on being a third pole in this political landscape. Another reason could be that, as splinter parties from the LDP, the other two are still seen as part and parcel of everything people dislike about LDP politics. Guilt by association. And of course, as conservative, nationalist, backwards-looking parties they compete directly with the LDP for the same voting bloc, but fail to give conservative LDP voters a reason to switch their support to them. Everyone's Party, on the other hand, seem to be tapping into a vein of urban centrist and liberal voters that aren't well served by existing parties. Time will tell if they can become the party of choice for that group, or if the DPJ will be able to peel them away.
#1 No, they're not courting health and exercise nuts, despite the name - and no, I'm not going to use their official English name of Sunrise Party when the original name is so deliciously silly. Especially as half the founding members probably need a cane or a walker to follow their own advice.