Okay, so it's taken me two weeks since coming back till I suddenly realised that actually I have some useful information to share...
One handy tip for anyone flying to Israel for a visit to Yad Hashmona - take a Nesher taxi from the airport. These are large shared taxis, with room for luggage, which cost 45 shekels per person instead of over 200 which you'd pay for an ordinary taxi. They operate from just outside the terminal, and drop you off right outside the guesthouse reception at Yad Hashmona. I used an ordinary taxi going there as I wasn't sure about the Nesher service, so paid much more and also had the added joy of having to hope that the taxi driver could find the way - whereas the Nesher drivers do this route regularly and won't look at you with a big question mark on their forehead when you say Yad Hashmona (Yad ha-what? where's that?). I used a Nesher taxi for getting back to the airport at the end of the conference - you can ask at reception and they order one for you for the time you need, and you are picked up from outside reception. Your luggage goes in the boot and you are then deposited with your luggage outside the terminal at Ben Gurion Airport. An excellent service!
Yad Hashmona is a small place and not everyone has heard of it. It's a lovely place with a good guesthouse. Unfortunately I didn't have time to explore the Biblical garden or the surrounding area, but I did enjoy the beautiful scenery and the lovely Jerusalem pine-filled air. Even the heat wasn't so bad there - in my part of the country you sweat all day in summer, but in the hills near Jerusalem the air is dry, which makes a huge difference.
The guesthouse is what they call chalet-style, which means the various parts of the guesthouse are sprawled around, not all in the same building - this means if you're not particularly fit you need to take into account that getting from your room to the dining room, for instance, may involve a short but steep uphill walk. (For me the real downside was literally the down-side, as I'm not very good at walking down hills - my vertigo kicks in. Anyway, I survived!)
The rooms were nice and comfortable, with an en-suite bathroom, a kettle (but disposable cups), a small fridge(!) and a television. (No real milk in the rooms though - just dairy-free coffee-whiteners. Liz, who had arrived with a bit more time to spare, ventured to a village nearby and bought some milk.) There was also a phone, which can be used for speaking to people in other rooms (useful when there for a conference) but I think you have to ask if you want an outside connection. At reception there's a computer with internet access which is provided for free, but they ask people to limit their use to 10 minutes at a time so that others may have a chance to use it.
Reception is also where there's a lobby area with tables and chairs where you can sit and chat, and hot and cold drinks for sale (including bottled water, which I found essential as the tap water just didn't taste drinkable to me) and a small gift shop (which also sells chocolate bars - how can you survive a conference without chocolate...).
The food (kosher) was good and very plentiful! And the approach to mealtimes is very laid back - no need to turn up on time as it's all self-service. Breakfast is Israeli-style, i.e. eggs, cheese, salads, etc, but also cereal and bread. Lunch and supper are both meat meals. There was always a choice of a few different main course options (beef/chicken/fish), and always tables overflowing with salads. (The downside of it being kosher is that at lunch or supper there's no milk for your tea or coffee in the dining room, just those non-dairy milk-replacements. But in the lobby you can have real milk.)
A very good place to stay if you want to be near Jerusalem.
http://yadha8.co.il