Dear Julian,
I hope you don't mind if I venture an opinion on this subject, as it's one I've been considering, too, having been writing the "Half- Dipper" for a while now.
The motivation really has to come from the fact that it's a normal part of your hobby - this is true for all writing, I think, not just blogging. I think you have to answer the following question very carefully, when thinking about starting a blog:
What are the primary reasons that you want to write to blog?
So, for example, my own answer to this question comes from the fact that I have a lot of notes, spread around a large number of hand- written books (my journals, in fact, which also contain my personal jottings). All except the most recent volume are kept in a wooden box, and they're quite inaccessible. To go back and find my notes on a particular tea is not an easy task. So, one of my main reasons for blogging is to allow a fully-searchable (and indexed) list of my thoughts on various teas - mostly wulong and pu'er. It also has the advantage over my journals in that I can include some photos of the tea itself, and that upon revisiting a tea, addenda can be created in a tea entry for new impressions that cannot easily be done for paper- and-pencil journals. As my readers will have probably noticed from the photos, I still keep the journals going, but I transcribe the results to the Half-Dipper afterwards.
That was my founding principle, but of equal importance are two other factors: the notes are, I hope, of some (albeit probably small) interest to others, in forming a rounded opinion of certain teas. If I am contemplating buying a new tea, I like to read around my trusted sources to canvas their opinion, and I hope that the Half-Dipper can fulfil this function for others, to some limited extent.
Last, but clearly not least, it's a great way to emphasise the communal aspects of tea-drinking. RFDT, the Pu'er Livejournal, Mike's pu'er forum and other dedicated fora are great cornerstones of the distributed (computer literate) tea-drinking community, but personal blogs are a great way to focus comments on particular teas, and randomly discussing other transient topics that pass through the authors' minds as they're writing their blog articles.
So, you've identified your reasons for writing - but how do you motivate yourself? I think if you explicitly need to make an effort to motivate yourself, then you probably shouldn't be writing a blog, with all the best will in the world. That is, if it becomes a chore and a grind, and you need to "push on, day after day", then clearly your blog has stepped out of the realm of being fun, and started becoming a bit of a burden. They say "a half-baked loaf satisfies neither baker nor eater", and I think this is true of blogs. My favourites are those that stay fresh and retain the passion of the writer, while those that slip to the bottom of my frequently-read list are those that are clearly becoming more of a chore for the authors. I think Tea Logic's VL has the right approach: when it shifts out of being a pleasure, and starts becoming a chore, then just take a break. Better that than pushing on, I think. Though everyone cried when Watterson stopped writing Calvin & Hobbes, they were better off in the long-run; their memories of the lovely, wise comic strip would not be quite so sweet had he pushed on and started churning out material while letting the quality slip (as with so many other syndicated comic strips).
I think one of the biggest sins of blogging is thinking that you have to write at a certain frequency. Instantly, you have created a burden of your hobby (even if the burden is light), and the beauty of tea-drinking becomes embroiled with an obligation to write another article for one's blog. Just to write when you have something to say, that is enough, I think.
"Keep it fresh", as a friend of mine likes to say whenever opportunity presents.
Toodlepip,
Hobbes