I bought a bunch of higher power (3 to 4 Watt) LED lights to see how they work with X10.
The PAR38, 4.5 Watt, 140 Lumen, 70 LED bulbs I bought off of Ebay for about 20 dollars a piece work just fine with one-way lamp modules and the socket rockets. The 4 Watt bulbs were equivalent to about a 40 Watt incandescent light bulb. You definitely want Warm White colored bulbs if you can find them since the standard white bulbs are a little more of a blue white than most people like. Some other types of LED bulbs didn't work with the one-way lamp modules since they wouldn't shut the LED off all the way which can dramatically decrease LED life. Bottom line is that in general you don't want to use dimming lamps or dimmer modules (2-way) with LEDs. Socket rockets are the way to go or in some cases the one-way lamp modules. Also, I had a hard time programming the socket rockets with LED bulbs in them. It's better to use incandescent bulbs while programming the socket rockets and then switching to the LED bulbs for actual use. Also beware that it seems difficult to switch the codes on the socket rockets after they have been used with LED bulbs. That's fine for me since I have my socket rockets programmed to several different address codes and don't ever need to switch them.
I now have most of my house converted over to LED bulbs and X10 control and am only using about 30 watts total for all of them. Huge power savings and the LED bulbs last anywhere from 60,000 to 100,000 hours which is many times more than the incandescent bulbs and they don't put off any heat which saves your air conditioning system too.
Just thought I'd share my results with people. I have about 10 extra of the 70 LED bulbs that worked with one-way modules and socket rockets if anyone is interested in them. Otherwise I'll sell them on ebay. If interested then email me at fuzz54@yahoo.com.