At $99/year I actually save $20 per year just by hosting one website through dotmac.
I have 4 websites that are hosted by my ISP. The first website costs me $15/month and each additional site costs $10/month in hosting fees. By moving just one of those sites to dotMac I no longer pay my ISP $120/year to host that site and Domain name, thus the $20 per year in savings.
That essentially means that all other dotmac services are free for me.
That's reason #1 of why DotMac is a great value for me.
Errr... whoa, you have some expensive hosting then? Need to look at something like Lunarpages.

$4.95 a month, unlimited Domain hosting, 1,500 GB storage, 15,000 GB/month bandwidth. I've used them before and am very happy with their service too. Comcast gives out free webhosting with their ISP service as well, but it's a rather skimpy amount per username on the account and very limited in uses beyond the basics. Before I'd pay for additional hosting through them, I'd go through Lunarpages.
In fairness, I never thought .mac was a great deal but MobileMe with it's various web apps. is a better value. I'm still not remotely in the market for it. That said, I still think that the major fly in the ointment for me is the lack of ability to host PHP or Ruby applications with an MySQL server. That said... that's not really MobileMe's market so I can understand them not including it. Most ISP web hosting plans don't either...
As far as 10.5.3... I've got it on 3 different systems. One Intel mini (came with), one Intel iMac 24" (came with), and one PowerPC G4 mini (bought as an upgrade). I think Leopard has run very well on all 3, better than Tiger even. It might have issues, but there have been people squawking at Apple about various OS X releases since OS X Developer Preview. There's been as many or more complaining about XP (vs. 2000) and Vista (vs. XP) since Microsoft shipped them too. People get stuck with things working a certain way and complain about changes. There's always a few bugs in each new system that take some resolving. For me... Leopard has had less than Tiger had when it first launched.
The only issue I have to date is the Intel mini's tendency to want to grey screen (kernal panic) from reboot. I've found that it's an issue with USB devices as occasionally it hangs unless I unhook/rehook the various USB and Firewire devices (including keyboard and mouse) on reboot. Otherwise, once it's up and running... it's solid as a rock.
Now if Apple could fix iTunes itself so that when I insert CD's that it doesn't mount/unmount them when performing an initial CDDB search I'd be much happier. I've found that the initial insertion does it but ejecting and reinserting for a second try always works. It must be some weird conflict of services with iTunes and the system itself.