Here are some tips that will help you get the best wireless connections using the WNR3500L, and also potentially, increase the life of the router.

In this example, I have 6 wireless devices attached from anywhere to a few feet away to up to more than 50 feet away on a separate level.

What you are looking for is a higher RSSI number in the connection.  So for example -25 would be way better than -75.

Also, don't be enticed into thinging that setting a higher transmit power will help you get a better wireless connection. In a lot of cases, all that does is make you chip run hotter and cuase more lost packets.

Router Orientation

First, do not lay the router flat. Here are my wireless connection statistics when the router is laid flat.

Now, here they are when standing the router upright.

You can see the close connections are about the same, but the farther away connections are better. 

Transmit Power

Now, let's change the transmit power of the router.

I am using Tomato at the recommended 42mW.  If you too are using the Tomato firmware, you can see these settings for your router at http://192.168.1.1/advanced-wireless.asp

To reduced heat and posible wear and tear on the router, what I want to do is lower the mW output.

So first, I changed the power setting to 5.

And here were the results...

As you can see, they did not change much, but with a lower mW setting the chip runs much cooler and you will extend the life of your router.

I then tried1 mW and lost a few connections.

So, there is a sweet spot that needs to be found.  In my case, it ended up being at 7 mW.

So, play with your transmit settings and find the sweet spot for your router and you should be able to not only reduce your wireless problems, but increase the life of your router.