I've had a plethora of problems with the Lexmark Impact S305 (b/g) since upgrading to Lion. They claim the new driver is 10.7 compatible, however I think not! I can print to it via USB with no problem - but wireless is an issue. It fails to 'find' or 'connect to' the printer wirelessly.
I updated the firmware (Lexmark_S300-S400_Series_E082511_00_FWUpdate.dmg) and installed the new driver (S300Series_X_1.0.172.dmg) but it hasn't solved the problem.
After resetting the Network Connection Device using the printer's buttons, and then running the Lexmark Wireless Setup Assistant, it's important to do a 'power-off reset' on the printer. What I mean by that - pull the power plug from it and leave it out for 10 seconds. At the same time, I did a power-off reset of my router, and restarted the iMac. After that - it worked! However, every time the printer goes to sleep, the problem resurfaces. Even powering the printer on (via its power button) before attempting to print doesn't help.
The only solution I've found is to do a power-off reset (of printer only) every time before printing. Big hassle - but it works. You have to wait for the printer to reestablish connection to the wireless network (indicated by the green indicator light on the printer) and then choose the print command.
I've communicated with Lexmark on this several times - they say there's a known issue with 10.7 and wireless printing - and "they're working on it"
I'll never buy another Lexmark!