Guys
I thought I'd share with you the solution that worked for me : I found that a cheap HDMI cable was the source of my frequent (30-40 times daily) wireless restarts.
If your router lives near a HDMI cable, you might want to experiment by disconnecting the HDMI (and taking it a long way away if you're superstitious!) and then monitoring your connection.
I replaced my cheap HDMI cable and I no longer see frequent restarts (although I still get one or two every couple of days).
(If you're wondering, my PC is connected by ethernet to my router and by HDMI to my TV - it's my media centre)
I hope that helps someone - it took me 3 full days of researching and trial and error to isolate the issue with mine.
Like others here, I must say that the old and cheap linksys WRT54 I swapped in temporarily while experimenting was not affected by this HDMI cable.
I also note that both the DIR-655 and the linksys are unaffected by the two DECT base units that are located very close by.
cheers
Paul