Interference from local APs - when is it significant?

[#1]

I'm using inSSIDer to check what local Wireless Access Points there are.
My AP registers a signal strength of -37dBm.
I've found about a dozen APs with strengths between -70dBm and -100dBm.
Presumably I don't need to worry about the APs that are using a different channel to me.
But what about those that are? At what power level might they be considered significant threats?

[#2]

Have a look at http://en.wikipedia.org/wiki/DBm .  You'll see that -40 dBm is a power level of 100 nW whilst -70 dBm is 100 pW.  Every 10 dB down is one tenth of the signal strength so a 30 dB difference equates to a factor is 1000.  Your broadband happily copes with being 6 dB above the noise level.  I think the problem is that these signal levels don't necessarily stay fixed.  If you watch them there seems to be a high-power "blast" every so often. 

[#3]

my problem is a nearby TalkTalk whose router is not satisfied with 3 chanels, thehy use 6, plus another a bit further away thar uses another six, so effectively two  users are occupying 12 channels, with the end ramps they are usinng 13

[#4]

It could be worth your while to get a dual-band 802.11n router and laptop, set them to 5.2GHz mode where you find far fewer people using those channels.
Also run inssider close to your router, as you want to know how loud the signals seen by your router are too.
Ideally, try to make sure your wanted signals are 10 or 20db greater than the interference if you want mostly uninterupted connections.

[#5]

5GHz has the added benefit of 24 non-overlapping channels.

[#6]

Thanks for all suggestions and comments.
I feel reassured now that other APs in my locality register so low on the power scales that they will not be an issue.
I can't see me splashing out on a new laptop and router anytime soon - my current ones are alive and well.