jvc57 had questions about ShoreTel. My experience with ShoreTel:

You'll see the history in this thread: Our 1st ShoreTel system installed May 2005. We purchase the hardware, I install 'em all. We are an end-user, not a Partner.

As of June 1 2007, ShoreTel statistics:
32 Sites are now ShoreTel. 4 of these sites are purely for Nortel interfacing. (We take care of 60 sites, overall)
5-6 more sites are due to be ShoreTel by Q4 2007 (including 2 of the 4 Nortel interface sites above)
70 ShoreTel switches are installed (ShoreTel switches, not LAN switches)
772 Extensions
547 Mailboxes (meaning ~225 devices not used by the typical every-day user. fax machines, lobby phones, cordless, etc)
1 HQ Server
2 Distributed Servers
We are in full license compliance

We have ShoreTel in 4 states
We are now a combination of ppp and MPLS circuits -- a big step to take over the last couple of years (remember Frame Relay, and frame of other flavors?)

We use Cisco routers, IOS release 12.1 or better for VoIP
We use some HP Procurve, mostly Adtran Netvanta PoE switches for VoIP
We use battery-backup at all VoIP sites (and nearly all sites, everywhere). PoE switches and battery backup means ShoreTel phones keep working during power outages
We use the ShoreTel IP530 (now discontinued) and IP560 telephones

Traffic May 1 to June 1, 2007
Total calls in the ShoreTel system to outside trunks 236,994
(Inbound 122,781, Outbound 114,213)
Total calls in the ShoreTel system that traveled over the WAN 38,714. Vast majority will be extension-to-extension
(Until we can find that great proactive and/or real-time network analyzing tool (that's affordable, and works), I am trying to be gentle on the WAN -- could allow a full Least Cost Routing to take full advantage of the WAN, afraid of overload -- don't have the time to monitor closely. May take baby steps one day, when (if) I have time to experiment)

By and large, I find our users love this system, and they spread the word. As I travel about our various locations, more and more people are exicted, aniticipating the day that they can be on this system

Trouble history
Most voice-quality troubles are Wan-based, some LAN-based, very few are ShoreTel hardware-based or ShoreTel software-based. (I think I could count on one hand the times I have had to call out for ShoreTel help)
I try to reboot all servers once per month to prevent trouble. Sometimes I'm not timely enough, strange troubles happen. Reboot fixes quickly. Not heavenly, but there are worse things happen in the world.
No real complaints. Does take closer watching of the network to keep voice happy, bad if you don't have in-house expertise, IMO. Not scary, new. Learning curve can be high for us old phone guys. Not insurmountable. Worth learning.