When a spirit switches between being Manifested on the physical plane and being in astral plane, does their Condition Monitor change size?

For example, would a force 4 Earth Spirit have 10 boxes in astral (8 + [F/2]) and 12 boxes (8+ [(Body of F+4)/2]) when manifested?

Yes.

EDIT: Of course, SCARed below is right, this applies to Materialization, not Manifestation. Thanks for catching that, SCARed.

if you mean materialized, then yes, the monitor does change. if the spirit just manifests (thus staying purely astral burt making himself kind of visible on the physical plane and able to communicate (with living beings): then no, the monitor doesn't change as he doesn't really switch planes.

Doh. Materialization and Manifestation are only a few letters different, but thankfully you guys knew what I meant.

So, essentially, if said Earth spirit was Materialized and had 10 boxes of damage already, then if it returned to the astral plane for whatever reason (and thus its condition monitor dropped to 10 boxes), then the spirit has effectively disrupted itself?

Yes, and since spirits not only prefer to remain astral, but prefer not to serve at all, going back to astral form would mean a quick trip to its home plane.

I know the relationships between summoners and spirits can be tenuous, but aren't there any normal spirits that actually LIKE serving people, so long as their services aren't painful? Ally spirits don't count because their formulae have loyalty built in (unless the summoner abuses them)

I get the impression that the act of summoning is like the magician either tricking the spirit into serving him or that there's some kind of mystical negotiation that takes place, a give and take. If a spirit is tricked, well, that would make sense why the spirit would tug at is bonds. But what if the service is beneficial to the spirit or a motivational factor?

"Hey, Spirit," the caster says, "why don't you come help me take out these toxic slots? We'll cleanse the taint from your brothers and sisters, purify the background count a little, and make the astral plane a nicer place for everybody. What do you say?"

Now, if I was a spirit, that's something I'd be game for. Give me some toxic shamans to burn, and I'd be happy to serve.

The relationship depends in part on the tradition the mage follows. In some traditions, the spirit is merely a tool, and if that 'tool' has any self-awareness, it won't feel any loyalty to the summoner at all. In others, there may be a stronger relationship. Take for example the traditions based on religious constructs, such as the Qabballistic tradition. A student of the Qabballah who summons an elohim may have a respectful dialogue with it that translates into a cooperative atmosphere. See below for more.

Then there are the Spirit Affinity and Spirit Bane Qualities, which have a strong effect on the way a spirit of the appropriate type will relate to the summoner. I suspect a player would build Spirit Bane into one of the spirit types his PC can summon only to have some fun with the back story.

The long-term behaviour of the summoner towards spirits may have an effect too. If the character continually does painful, nasty things to spirits, then, on the way to developing a Spirit Bane, he may discover that they work the letter of the contract more closely.