Have you looked at the 10.7 Performance Monitor built into your Mac?
What do you get for signal and noise when it is running?
Click on the blue text in my post above. This will take you to an article that explains how to use the built-in performance monitor tools in 10.7.
To get the application, simply open your hard drive and you will find the System folder. From there follow the path below to find the Wi-Fi Diagnostics application.
Use the performance monitor portion of those tools to note the typical signal level and the typical noise level. Also note that the graphs should be flat (no spikes).
Monitor Performance displays a graph of network signal strength, noise level, transmit power, and data rate. Information such as Country Code, SSID, Channel, txPower, txRate, Signal, and Noise are logged and displayed in the area at the top of the window with each line representing a single sampling. The graph below shows a running representation of the wi-fi networks signal and noise measured in dBm.
Then use the information in this excellent User Tip by tesserax to evaluate your signal to noise level:
- 40+dB = Excellent signal
- 25dB to 40dB = Very good signal
- 15dB to 25dB = Low signal
- 10dB to 15dB = Very low signal
- 5dB to 10dB = Little or no signal
full User tip is here: Airport: Optimal Base Station Placement
That's not "just fine".
The first part of the graph shows -60db signal and about -85 to 90 noise. That gives you 30 to 25, which is OK. Then in the last third, the signal deteriorates nearly 10db and the noise gets higher, leaving barely 20 signal to noise. That is considered weak.
If this is what you found on a random look, I would be very concerned that in steady use, the signal would drop off more and the noise would get higher, causing your connection to seem very slow.
How many other Routers are around you?
If that tool does not tell you, the free utility iStumbler will:
Do you have a dual-band Router, with channels above 11?
If not, there is comfortable space for three networks in the 2.4GHz band (channels 1..6..11), and you can sometimes cram in six and still work.
With a dual-band Router, you get dozens more channels and you get away from all those others.
19 is simply too crowded for good stable results in the long run.