I figured I'd chime in, because my experience with the WRT54G is similar to others. I've had this router running without a cold reset for about 8 months... and then I got my MacBook Pro.
In the house, everything seems OK - but if I step out on my back deck, the signal drops instantly on the MBP down to one bar. Usually after a few minutes, it drops completely. And since I don't broadcast my SSID, the MBP doesn't pick up the connection when I move back into the house. I have to manually recreate the connection and then all is well.
I have never had a problem with any of my Dell notebooks (and I've owned quite a few, some running Windows, some running Linux) in any part of my house (inside or out). But the MBP just doesn't seem to have the same range. Not a biggie, but annoying nonetheless.
Just so you know, my house is about 2300 sq. ft and two stories. The router is located on the second floor in my office. My house is fully wired for ethernet (cat 5e) and everything terminates in a patch panel in my basement. Almost every room is wired for ethernet. My cable modem is mounted on the wall in my basement and connects to a Linksys gigabit 6-port switch. The WRT54G is patched to the gigabit switch.
This setup worked flawlessly up until now. So far, I've ensured that I'm up to date on firmware, experimented with different channels, repositioned the antennas in several different ways and used Netstumbler to try to determine what other signals might be intruding. I've made sure that my router is set on a distinct channel from the other routers in the area. I'm in a fairly rural development, so there's not a lot of neighbors around and I can only sniff a faint signal from 3 other routers - all of them Linksys (believe it or not).
I like Linksys because they're owned by Cisco and I administer a network professionally that is comprised of all Cisco devices. I like their products and have always held them in high esteem.. up until now.
Linksys support for Mac is non-existent. I've never had to call their tech support line and I don't intend to since I probably know networking better than most of their tech support staff (I know, that's not saying much).
My next course of action is to move the Linksys to a different, more centrally located room that is not on the extreme side of the house, but I'm starting to think that maybe I should consider a different model. Since the house is wired and I'm a tech-head, I do intend to take advantage of the network to its fullest. When 802.11n becomes a true standard, I'm thinking I may upgrade everything anyway. I'm seriously considering a D-Link DIR-635 (I don't care for the antenna-less design of the AirPort Extreme). Anyone have any thoughts on this?
EDIT: Oddly enough, after writing this thread, I decided to adjust my antennas a bit and adjust the channel - and sure enough, I'm seeing better signal outside, on my deck. Maybe I will hold off on that router upgrade for a bit. I've been considering the optional high-gain antennas, maybe that will be my next step.