Couple points....
1. On the Support side - we cannot realistically sell open-ended entitlements; next to fundamentally being a kind of "insurance" from a business model perspective, keep in mind that this is also a type of "voucher" from a accounting perspective and the bookkeeping on the balance sheet if they would be good forever - or even just for longer than a year - are somewhat problematic. You may be able to discuss with our sales department if they are able to give you a quote for a subscription that includes some support per year.
2. Obviously if a support issue is found to be a bug, you won't get charged any support points and can re-use them for another situation. Again looking at the expiry, keep in mind that we're working through the issue anyway in Tech Support, investigating. And if something is found to be a severe bug affecting you badly, the fact that you have (a) a valid support entitlement and (b) a valid subscription allows the support agent to open an Escalation on your behalf, which may result in a hotfix being prepared for you. So I really don't want to discuss this from a cost perspective, but I think all-in-all you get a pretty good general value out of Scalix' services offerings.
3. On the Mac side - it's a difficult beast. I do use a Mac (or actually several of them) and with my 7 GB+ mailbox, Mail.app works very, very fine, stable and performant for me with Scalix 11.4.3, no mailbox reorg required in a long time.. iCal is a mixed user experience, partially because it's still improving. I've had direct chat's with the product's developers @Apple and they acknowledge that the product and it's CalDAV support has some issues on their side as well, although it's improving. The non-auto-completion of the addresses is probably the most severe limitation, this, however is by in large outside our control. Apple chose *NOT* to use their own Directory Services LDAP switch API and/or Address Book access API as for Mail, but as soon as you run iCal.app against a CalDAV server, it silently believes that it's talking to Apple's own Calendar Server, then furthermore assumes it is connected to Apple's Open Directory, and then relies on a very proprietary and not fully documented private LDAP schema to do it's lookups. So until this changes from their side (and rumor is that they are planning to do so, however will never formally commit!), the only way to support his would be to fully reverse-engineer and emulate their schema, and that's not really our plan and concept of implementing "Open Standards".

Please write them a letter as well what you think about that part. The more they read it, the more they may actually listen, eventually.
Just my thoughts....
Flo.