I would get reservations. All you need is a major trade show and everthing in town will be booked solid.

I agree that you should make reservations. There is a city planners' meeting April 14-17 that will bring about 5,500 to town. A retail display and marketing show April 16-18 is expected to draw 150,000, a biotech meeting April 22-25 is expecting 16,000 attendees and a comic and entertainment expo April 26-28 is anticipating 40,000 people. In addition to these, there are several smaller meetings that will each bring between 200 and 1,000 people into the city during those periods.

For the river cruises, you can usually get tickets a day or two ahead of the date you want, then you'll know the weather.

For restaurants and other events, check www.chicagomagazine.com or www.chicagoreader.com. You can search for restaurants by cuisine, price or neighborhood.

You may consider Signature Lounge at the 96th ion the Hancock building. Instead of paying for the Willis Tower for the observation deck you can have a drink at the Lounge with a free ride up. Gorgeous views and a drink with comfortable sitting. They also have a restaurant on the 95th floor. Just make sure it's a clear day/evening.

http://www.signatureroom.com/Signature-Lounge/

Second City sells out weeks in advance. The boat tours probably will not but if you do need 8 tickets they may not have room. For sure make restaurant reservations.

Hub 51, Mercadito, Slurping Turtle and Purple Pig are some of the best places in River North.

http://chicagovisitor.net/Restaurants.html

Don't forget Chicago pizza. Gino's East is my favorite, but it's hard to go wrong.

Second the Signature. You may want to go up right at 5 when it opens (confirm that time) to get a seat in the lounge next to the windows. That said, we did the Willis with the glass balconies. Expensive and a bit cheesy but also kind of a neat experience.

Not in River North but not far: The Berghoff (German food). Some good restaurant and other tips on this thread (but keep in mind it was specific to Christmas time):

http://www.fodors.com/community/united-states/chicago-christmas-trip.cfm

Fewer cruises just means that they book up faster. If and when the weather permits. Although the further you get into April, the less likely it is that snow will occur; but then you have to consider the spring storms, which can be devasting in their own right. So, my suggestion would be to wait until three-to-four days out, keep checking the weather forecast and get reservations (if you can) as soon as possible if it appears the weather will cooperate - as there are no refunds once you purchase them.

Likewise, a visit to the Willis Tower (the above poster is referring to the "Ledge") would not benefit you if it is foggy or severly storming. Nor is dining at the Signature Room.

Yes, you'll probably need to purchase tickets for Second City weeks in advance - especially on weekends and/or for long weekends.

Please keep in mind that when your party is 6+, normally there is a gratuity fee of 18-20%+ automatically included on your bill. If you check the menus online, they'll usually point out their requirements.

With all due respect to the above responders, you are coming to one of the great dining destinations in the world. Why limit yourselves to only the area near your hotel (which is, quite frankly, one of the most highly frequented by tourists)? Although some of Chicagofan's suggestions are good choices, IMHO, you can do better than that.

Especially since some of the greatest choices for evening entertainment is *away* from the Mag. Mile, River North and Loop locations.

I apologize for my poor proofreading skills above. However, I'm sure you get the meaning.

To continue with my last paragraph...What I would suggest is that you take a look at the evening entertainment available when you are here. This could be theatre, dance, comedy, music, concerts, etc. You can use a number of different websites: the Chicago Magazine, Chicago Tribune, Chicago Sun Times, the Chicago Reader, Time Out Chicago, Choose Chicago, etc.

Then, once you have chosen (and you'll see that many, many more choices are in outlying neighborhoods other than River North, Mag. Mile and/or the Loop areas), chose your dining option in that specific area. Many of these same websites have articles and blogs which give "best of" lists as well as outlines new restaurants and gives reviews. I would also recommend a quick glance at Yelp.

Check out N. Wells Street ( Division to NOrth) for a variety of good restaurants, near Second City.

Thanks to everyone for such great suggestions. All of this information is very helpful!