I see and hear so many things and have read some rotten reviews about Flybe, but I have just used them again this past weekend and have to say I have never had anything but excellent service with them.
I use them several times a year flying from Southampton up to Manchester. I always fly on a Saturday morning (the 8.50am flight) and return from Manchester on either the 5 or 8pm flight. Only once I have been delayed in Southampton but that was only by 10 minutes, which we made up on the way, therefore meaning I landed at the specified time. I wish I could say the same for Air France who I used from Southampton once and who cancelled not only the flight I was booked on at 6am, but also the next 3 meaning we finally took off at 8pm that evening (there really isn't enough to do in Southampton airport for that long but go totally stir crazy).

I've heard people moan about needing show ID to get on the plane when just using them internally. I'm not sure this is just a Flybe thing. I imagine it's an across the board thing that all airlines now employ due to security and it's really no big deal taking along some form of ID. I always use a passport as it's the only thing I have with my photo on. My friend was able to use her driving license. Surely it's better to carry an extra piece of paper in your bag to show who you are, than it is to risk a security issue? A downside to them is on board hand luggage. If you check out the sizes on their website you will see that they have a smaller allowance than the other budget airlines, but to be honest as long as your bag can be squeezed into the tester bits at the airport you should be fine. Don't think this will mean you bag will fit in the over head lockers though. This time I flew up with a friend whose bag fitted in the test area perfectly, but we really had to jiggle and squeeze it about on the flight up to Manchester. Coming back we were on a bigger plane (don't ask me what planes they are as I have no clue - they used a propeller going up, and a jet engine one coming back).
In comparison to most food outlets (parks, seaside booths etc) their prices on board for teas and coffees is on a par. Yes dearer than I think they should be, but then most places over charge for the basics these days, so it's to be expected. The coffee is hot though so what more do you need?
I've never used the toilet on board (not really worth it for a 40 minute flight) but I've been told they are clean enough.
The flight attendants I can't fault. Flying up on Saturday my friend realised she had left her jacket in the airport, so the attendant radioed through for her and had her jacket collected and delivered to the plane before we took off. I have also seen how great they are with disabled passengers and it's this attention to detail that really makes the difference between good crew and great crew.
For a budget airline I personally think their seats are great. They are comfy and have a really good amount of leg room (far better than BA planes of a similar size where your knees are tucked up under your chin).
The jet plane on the way back almost made us feel as if we had been upgraded there was that much leg room (far more room in the overhead lockers on this plane too).
The information given out by the flight crew and captain with regards take off, flight time and landing is good and I've always been able to hear what is being said (which is more than I can say for some passengers who seem to think it's their right NOT to have to turn their phones off when it comes to take off and landing - this really annoys me as they may feel the airline are being over protective, but I would rather this than end up in a crumpled heap somewhere on the M6. Personally I don't think anyone should be allowed to use a phone full stop on a flight, but that's just me. I'm sure people can last 40 minutes without having to share their calls with a plane load of strangers.

I love the whole online checking idea. I never travel with more than a carry on bag as I am often only in Manchester for 2 nights, so to be able to check myself in from home the night before, saves me so much time and makes life just that little bit easier. We arrived a Southampton with an hour to spare on Saturday but with it being a bank holiday it took us forever to get through the security part (we literally got though and boarded so you can imagine how long it took). If we had, had to queue to check in as well we would most likely have missed the flight completely.
The only thing I do really object too with them though is having to pay £6 per person, per flight for choosing the seat I want. Especially when we flew back on Tuesday evening to find the plane was only about 20% full which meant we could pretty much have sat wherever we wanted. Annoyingly we had already handed over £12 so that was really annoying. Other than that I really can't fault them.
If you haven't discovered already, FlyBe's carry-on baggage dimensions now match many of the other low-fares airlines, effective July 2012r. Also when I check-in at the airport (no additional fee!), the check-in personnel have been pleasant and have always tried to accommodate my 6ft+ frame in a seat that's got some legroom, no extra charge (flying on the lowest economy fare, too!). FlyBe do make you feel wanted, unlike some of the low-fare airlines. Nice review!