I had a few issues with it to try to get it to work. It seems that the first time needs a little longer to recognise the other touch (at least for me). Try to keep the object on the screen for a longer while so it can scan the object better. After a while it just worked with pretty much anything. Which is great for when i'm walking the dog and wanna browse for some news (to not get bored).
So if you have trouble: try to keep it on the screen a little longer. If it already worked a while ago. Try to turn the screen on and off again. (worked with me on another occasion). No need to reboot, just hit the powerbutton to turn it off and back on again.
This suggestion does work for me in a way. If I turn the screen on/off a few times, it eventually responds. Also if I hit volume-down to extend the time the screen is lit up a couple of times, again it eventually responds. It's inconsistent in that sometimes it works quicker than others.
However, shouldn't it activate reliably without having to use these workarounds? Once it has "activated" it works perfectly until next time it's locked. But getting it to activate is very hit and miss and can take anywhere from 1 - 15 seconds.
Martinspire -How long did it take approximately before it worked with pretty much anything?
On a side note, I got the 1308 firmware update yesterday through official channels - doesn't seem to address this issue.