I always play with Arsenal, and as I am a huge Arsenal supporter, and I cannot imagine playing with anyone else but Arsenal. Therefor I do not do "challenges", "scenarios" etc.
I always have the game loaded on my work laptop. The reason is that as a Divisional Systems Trainer I am always very early at my Training Centre and I can get a good 30 min or so of playing time in. The other reason is that I use the game as entertainment if I am involved with the opening of new stores (I work for the largest Retail Company in Africa) that require me to stay over, or if I have to travel to another country for Training purposes.
I always play the game in Windowed mode. Therefor after hours I can play the game, watch my work mails, do store system support, while I keep an eye on the laptop, and the TV, whilst still making sure that I listen when my wife have something to say! (I used to be a Branch Manager before my current position, and this enable me to be very good at multitasking)
I can play this game for hours and not get bored. I normally play till 23:00 every night, if I have one rest day during the week (normally a Sunday because of church sermon and the possibility of a afternoon nap!) I normally start one saved game, and continue with this until the next release. Even if the database gets updated, I will not start a new game. My saved game in FM12 was 110 days playing time in total (19 full seasons).
My favourite part is scouting for regens while they are in their first club, to buy them cheap, mould them, keeping the best of the best and selling the rest for as much money as possible with a 50% share of the next transfer sale clause included.
I love this game. I have been hooked, line and sinker a long time ago already. No matter how many "problems", or "issues" there is with every version, I'll still buy this game, every year. SI always find a way to rectify it (even stuff that I did not noticed or thought was a problem), and always find a way of improving the game, year after year (well at least I think so!)