I own the same bike (1989 Cannondale 3.0 with Dura Ace) and it is a very nice bike. I use it for commuting as well.

It is a very stiff frame, being aluminum with large tubes. This means the ride is quite "harsh", meaning you feel all the bumps in the road. The front fork is steel, to absorb some of the bumps.This also means however that it is a fast frame, transfers the power from your pedals to the wheels well. You can mitigate this by using thicker tires, giving a smoother ride.

It is not the lightest bike by modern standards, might be around 20 pounds, don't expect a featherweight road bike like a new carbon fiber bike that costs $2000. For the price however, you won;t find anything lighter, not even new bikes.

It has downtube shifters, so you have to move your hand to the downtube to change gears, which is less convenient than modern bikes, which have shifters on the break levers. You could always upgrade the bike and put on more modern though, so that shouldnt be a dealbreaker. Personally I like the vintage downtube shifters.

It has Dura Ace components. Dura Ace is the top-of-the-line groupset (shifters, derailleur, brakes, crankset, etc.) from Shimano. This means higher quality, longer longevity, so hopefully not worn out yet.

It seems to be in good condition, so $350 seems like a fair price. I like the color as well! Many people love these bikes, and they are considered a legendary frame that was the top-of-the-line back in its day. They are beautifully handmade in the USA, with very smooth welding on the aluminum (compared to factory mass-produced aluminum bikes nowadays).

Be sure to test ride it, that looks like a large size frame. Make sure it fits you.

Get it! I think you wont regret it.