Hi Irogersinlv,
Since you posted this last week, I too had the wifi issue once I upgraded to OS X Lion. After a week of trouble shooting with various Apple Support team members, I may have solved this issue for me and I hope that this may give some of you some ideas of what you can do for your situation.
First, please note that I did try everyone's suggestions here, i.e., deleting plist, moving wifi to the first location, changing my DNS to 8.8.8.8, resetting my router, creating a new connection etc. I tried all the suggestions here (thanks everyone). I was scheduled to bring my iMac 27" (bought in December 2010) to the genius bar but had scheduled to speak to an Apple Support team last night. She tried all the suggestions we all tried here at the forum and nothing worked. She asked that we do a clean re-install of OS X Lion from recovery mode just to start from the basics. I had to connect via hard wire ethernet and then the download started. It stated that it would take over an hour so she scheduled to call back this morning.
After the re-insstalling of OS X Lion, I first pulled the ethernet out of the back and tested the connection. Yes, it did work but I knew better; I decided to restart my iMac and once I wanted to get back on the internet it did not work via wifi. Still shoing FULL BARS but no connection. I resetted my Dlink DIR-625 router, my modem and switch box and it seemed to work intermittently. I was puzzled as by this point, I had tried 2 Dlink DIR-625 router, exchanged my modem and nothing was working. I asked my neighbor if I can use thier Linksys wifi and tried that, It worked??? Can it be something with dlink's wifi router DIR-625? I tried the Linksys for several hours with success so decided to go back to the dlink and then the connection started to fail again? I did some research on this forum on OS X LION AND DLINK and found that some people were having some issues with OS X Snow Leopard and the Dlink DIR-625 model. Their successful solution was to change the settings in the wireless router to select b/g NOT the n setting
This is the suggestion that I got off this forum by doing a search for MAC OS X and Dlink DIR-625:
https://discussions.apple.com/thread/1394194?answerId=6648782022#6648782022&messageID=6648782#6648782?messageI D=6648782
This suggestion from this user worked for me. It has been over 6 hours now and I'm still able to now get my wifi connection. I tried shutting down, restarting several times and with changing the settings to select b/g only, it has been working for me so far. I know that this may not be the end all be all answer that you maybe looking for but I hope it may give you a direction to try. I will continue to test and hopefully found a solution that worked.