I use usbnet to connect to Internet via Linux PC.
When usb0 up I set /etc/resolv.conf on tablet.
But loaded applets (for example omweather) used old DNS setting.
I have to restart hildon-desktop to tell omweather use new nameservers.
Do anybody know easy way to inform loaded applets use new DNS?

You should not change /etc/resolv.conf. This usually includes only 127.0.0.1 which makes the installed local dnsmasq server. Just point dnsmasq to the correct DNS server by editing one of:

/tmp/resolv.conf.wlan0
/tmp/resolv.conf.ppp0
/tmp/resolv.conf.lo
/tmp/resolv.conf.wimax0

if i use usb0 - /tmp/resolv.conf.usb0?

i run a named server on my network. i want my n800 to use that for DNS, which it does when browsing the web, but when i want to ssh to something, i have to use ip because the DNS doesnt resovle. why isnt this standard compliant?

i do not have any of the tmp files you specify (on my n800 with diablo). should they be created?

what does dnsmasq do and why is it interfering with normal DNS resolution?

dnsmasq solves exactly the problem of resolv.conf changing while application is running. As far as all applications are concerned the DNS server is 127.0.0.1 (this is always in /etc/resolv.conf, regardless of network connection). This way only dnsmasq needs to be aware of DNS server changes (as a result of network connection change, for example).

dnsmasq gets the server information in the files I listed (see /etc/dnsmasq.conf). If you are creating another connection, the easiest way is to use one of those files, even if it needs to be created.