For the first week, I just kept it in my pocket while I followed my normal routine, and that established a baseline. After that, the website gave me targets each week (starting at 5000 steps per day), and if I met that target then it would be a bit higher the following week. That went well, and it did motivate me to do a bit of extra walking when I had a specific goal in mind. I now have a pretty good idea of how many steps are involved in common routes (e.g. 2000 steps from my flat to the railway station), so I can plan out when to walk and when to take the bus.
The problem came at the start of June, when I was given 10100 steps/day as my new target. I'd assumed that I was working my way up to 10000, since that's the well publicised target; I suspect that it's a bit arbitrary, but it's a nice round number, so I'm happy with that. However, since my daily target was higher than that, would it just keep rising indefinitely? There comes a point where the amount of walking I do in a day is limited by time more than fitness, and 10000 steps takes me 1 hour and 40 minutes (if I average 100 steps/minute). So, this new threshold basically killed my motivation; I haven't even bothered looking at my targets in the last two months. Instead, I just keep an eye on the total, and decide whether it's feasible to do enough steps to earn points.
As for the points, is it justifying the cost? It's a bit tricky to assign an exact value to Vitality points, because they work on thresholds; there's no difference between 1 and 999, if I'm still below 1000. However, based on the discount at each level, each point is roughly worth 29 pence. (The full price for my plan is currently £48.52/month = £582.24/year, and 2000 points gets me a 100% discount.) So far I've earned 110 points from the 'bug, i.e. £32. Putting this in context, the gadget cost me £15, so I've already recouped my investment and saved an extra £17. At my current rate, I'll get 264 points by the end of the year, i.e. an extra £45. Also, I'm walking a lot more than I was 5 months ago, so that figure may be higher.
There's also the knock-on effect of increasing my general fitness. Apparently 10000 steps ~= 500kcal, so if I can burn extra calories by walking and then slim down, I'll earn extra points that way. (I recognise that some people dispute the link between food/exercise and weight, but I'm willing to give it a go and see what happens.)
So, this comes back to the issue of adjusting my routine to include the extra steps. One simple approach is to walk instead of taking the bus; the downside is that it takes longer. That's ok if I'm coming home from work, but it's a bit more tricky if I'm in a rush in the morning, especially because my commute is a bit fragile: when I change trains at Clapham Junction, there's only one train every 30 minutes. However, even then walking can be good, because it's more reliable. Simplifying a bit, my typical journey to work would go like this:
07:30 - catch bus to station (arrives at 07:40).
07:45 - catch first train (arrives at 07:55).
08:05 - catch second train.
That's fine, but there's a 10 minute gap between buses; if I miss the one at 07:30 (or it's late/full), I miss my first train, and then I have to wait half an hour for my second train. An alternative is to aim for the 07:20 bus, so that I have more margin of error. However, it only takes me 20 minutes to walk to the station, so if I'm leaving that early then I may as well just do that instead, which gives me complete control over my arrival time (no traffic jams). This still relies on me actually getting up early in the morning, but I'm working on that, and extra exercise helps to make me tired in the evening. (I realise that would be more convincing if I wasn't typing this at 1am!)
The other odd quirk comes at the end of the day. From the bug's point of view, each day runs from 00:00:00 to 23:59:59, rather than "the time I get up until the time I go to bed". Tonight, I'd already done 7500 steps, so that just left me another 2500 to get the points; if I go to the recycling bins and back, that's 3000, which takes me about half an hour. I was watching TV (Stargate Continuum, very good), so I couldn't leave until 23:40, and I didn't have enough time to get there and back. However, I didn't actually need to be home by midnight, I just needed to do enough steps to hit the 10k threshold before the clock ticked over, even if I was halfway down the street at that point. The extra wrinkle is that I can't watch the step count as I walk; I need to keep the bug in my pocket, otherwise it doesn't count properly. I did stop to look at it a couple of times, but then I was burning valuable seconds. Once it got past midnight, the step count showed a much smaller number, but I couldn't check yesterday's total until I plugged the bug into my computer: 9974. So close! Ah well, those extra steps aren't lost, since they count towards today's total, and it is good exercise even if I don't get rewarded for it.
Anyway, all in all I'm happy with the bug, so I think it was worth the money I spent on it.
Edit: Corrected my figures - I had monthly/yearly costs mixed up.