I was having connection problems with my cable service with no seeming explanation, all the phone techs could do was to think of 30 ways for me to reboot everything in the house. Good thing they sent a tech out. Turns out the signal strength to my cable modem was weak because the guys who installed cable in our house broke one of the splitters so it was 'leaking signal' [a bad thing also because according to the cable guy it can make it look like you're stealing cable]. Anyway a new splitter and no more intermittent connection problems.

Turns out the numbers were right in front of me and I could have diagnosed the problem. In the modem admin interface there is a Cable > Signal area with the following information:

Downstream:
Signal to Noise Ratio 40.3 dB
Power Level -2.7 dBmV

Upstream:
Power Level 52.5 dBmV

Right now the values are OK. Depending on your modem model and who you listen to here are some guides for what 'ok' values are:

Downstream:
S/N > 30 dB
Power Level -7 to 7 dBmV (mine was -12 when the problems were happening)

Upstream:
Power Level < 55 dBmV

I can't find this information in the manual for my modem but hopefully if you're having similar problems you can find the numbers more specific for your modem in your manual or by searching.