I am an involuntary
* Comcast customer. So yes, Macs work just fine with Comcast.
Regarding the (totally separate) Linksys issue, well...
In the years prior to Cisco's purchase -- and then eventual degredation -- of Linksys' line of wireless routers, they were one of the best pieces of equipment you could buy. They retained this status through the first three or so iterations of their G-class router. They then switched to a different firmware (VxWorks) and drastically scaled back on on-board RAM. They also speed-bumped the CPU. All these things (plus the fact that Cisco/Linksys is producing much higher-volume numbers of these things than they used to -- or that Linksys ever did) are contributing factors to the decline in product quality, equipment longevity, and even serviceability.
This really isn't totally the time and place to get into it fully, and it
has been discussed before here at MacRumors.com, but one of the things I recommend to people with Linksys WRT54G and WRT54GS series routers is to investigate the open source-produced replacement firmware for your routers. They are, respectively, the
OpenWRT Project and the
DD-WRT Project. Now, I won't lie to you: of the two, my own personal preference is DD-WRT, but do your own investigation and decide which is best for your own needs.
* I was a Time-Warner (a.k.a. "RoadRunner") customer until Comcast swapped territories with them. In order to keep and have cable and cable modem service, I have little choice but to use Comcast.