I am having the same issue since Saturday. I have worked for 90 minutes with my ISP Verizon FIOS on this. I have done the following
Cleared SL cahe
Cleared all brower cache and have done disk cleanup.
Reset the factory setings on my router
Disabled all firewalls on my router, within Window 7 and on my Antivirus
I have just now tried to log into the Smith & Lime region and still could not get in.
I went to an internet cafe less then 5 miles from my house on Sunday and was able to get on SL
The last resort is that Verizon is shipping me a replacement router. I will switch my router out on Wednesday and see if that works.
Does anyone have any other suggestions? Maybe there is something wrong on Second life's end?