My wife has been with then for 4+ years, and I moved myself in the fall.
First off, any opinions you hear online from people who haven't been customers in the last year (at least), if not 6 months, sorry, but IMHO, discount those opinions. The network has changed *dramatically* for the better in that period, and especially in the last 6 months or so. People that tried it 2 or 3 years ago (and are no longer customers) likely have bad memories, not exactly unjustifiably so (again, my wife went through it, but we saved about $3000+ vs what she was paying before in that period!), but it's WAY better now. Still a lot of people sharing those bad memories though, even though they don't really hold true anymore.
That said, are you going to get Big3 level of service? No. But if you're willing to put up with a little bit of growing pains to save a lot, then it's a great option so long as you understand their service footprint - they are an urban carrier. Many of their new plans do include a small complement of roaming minutes and data, but the allotments used to be bigger than they are now. But, if you spend most of your time in their service area, well, different story.
If you can go to a retail store and find an employee willing to put you on the old $50 plan that was around just before the introduction of the big-gig plans, DO IT. 8 gigs data, unlimited Talk/Text/MMS/Long Distance, 1 Gig roaming w/2400 minutes and unlimited text roaming...USA included. They're not listed anymore but rumour is they are still in their system as being available if you find someone willing.
My wife and I are both on these $50 plans and coupled with a 30% Friends and Family discount on both lines (Google it, it's a long story) our cellphone bill is $67/Month total.
What I like most is that I no longer have to care about overages anymore. If I use all my data, it still works, it just slows down. If you use a grossly excessive amount, it slows down some more...but it still works, and NO extra costs. Knowing that our bills are going to be the same, all the time, every time is worth it in my books. I was getting tired of $130-$150/Month bills with Fido so as soon as the network matured enough that it worked for me (my wifes needs were less so she was able to make do the last 4 years) I jumped ship from Fido and have never looked back.
Ultimately, I tell people to do what I did - go get a SIM and sign up for an account with a temporary number, pop in the SIM, and actually use the service for 3-4 days and see if it works for you. If it does, you can port your number from your existing carrier (the temp number will just go dead and your SIM will switch automatically) and you're golden. If not, you cancel the service, pop your old SIM back in, and you're only out a few bucks and none the worse for the experiment. Win win, IMHO.