I have a somewhat different take on the "boringness" factor of Phoenix. Believe it or not, I think there's actually more to do here at night than there is during the day. Mill Ave, pretty much any night of the week (with the exception of Sunday night, for some reason) is a happening place. You can always rely on the quirky characters and street bums there to get a few free laughs. If you're a drinker, between Tempe and downtown Scottsdale, you've hit the jackpot. There are countless bars in the area, many of them outdoor bars, like Dos Gringos, Flickas, Sugar Daddy's, Salty Senorita, Los Sombreros, Loco Patron. Ra Sushi, with a bunch of locations, is pretty popular. I've never been there, but I heard Alice Cooperstown in downtown PHX is pretty cool. There are also some coffee shops that are open 24/7. Downtown Scottsdale in particular is emerging as a center of nightlife. There are a couple of hip dance clubs in the area, places so hip I doubt I could even get in.

In Mill Ave and Old Town Scottsdale, there are an increasing number of late-night eateries open. Then when you throw in the Improv in Tempe, the Marquee Theater, the Clubhouse, plus your normal Harkins theaters, Gameworx, and Dave and Busters, you have an impressive selection of night life.
Thing is, I'm not a drinker. I am 21, but I think drinking is stupid, and not very fun. So that right off the bat excludes me from at least half of all the things people my age do here. I'm also tired of going to "keggers"-- trashy house parties thrown by college kids living in rental houses (half of which get shut down by the Tempe PD). I'm more of a day person than a night person anyway. I've found that during the day, Phoenix can be very boring-- frustratingly so. I like bicycling and hiking, but what I've found after living here for several years, is that for 3/4 of the year, it's too hot to do those activities during the bulk of the daylight hours. This time of year, for example, it's great at night, early morning, and late afternoon, but between 10:00 and 4:00 it STILL feels too hot to be outside for a long period of time. No cloud cover to filter the sun's rays. It feels great when you're outside for a minute, walking across the parking lot to your car. After a few minutes, it gets uncomfortable. I'm also trying to be extremely careful about not getting sunburn.
One of my favorite things to do is just go exploring. I'm at the point with Phoenix where I feel like I've just about explored pretty much every part of town, everything in central Phoenix, Tempe, Scottsdale, and Mesa that's worth seeing. Truth is, there isn't much. I've walked around downtown many, many times, for fun, and I'm usually depressed by the time I'm through-- depressed at how "empty" it feels. It feels like a ghost town with big buildings. The central Ave/ uptown corridor is even worse. BTW, I think that the PHX art museum and the Heard Museum are great institutions, but I think the PHX Public library is one of the worst libraries I've ever seen. Cool building, but hardly any books in it. I've heard people say how the Biltmore area is so cool-- well, I went there again last weekend and I was bored out of my mind. A generic shopping mall and some office buildings. Yawn.
During the last few months, I've actually been "exploring" strip malls for fun-- on bicycle. I've also bicycled through some pretty ghetto parts of Phoenix-- just for the adrenaline rush.

I've bicycled through countless neighborhoods-- I haven't seen it all, but I think I've seen a pretty good assortment of what Phoenix has to offer. Sometimes I'm so bored I just drive around-- which usually makes me even more bored than I started. When I first brought my car down here, I thought I'd be taking trips to places like Sedona and Flagstaff every weekend. WRONG!

The traffic on I-17 trying to get up north (and back at the end of the day) is so horrendous and so dangerous, I've about given up on that.
So I'd say, in terms of night life, Phoenix gets a B+. In terms of day activity, a D-.