I can say that I have a foot in both camps having setup both sharepoint and Moodle, I've got to say I prefer Moodle.
The school I work at had a working sharepoint environment with the SIMS Learning Gateway (SLG) modules attached. It worked but it was tempremental as hell; teachers would lose whole reports simply because they didn't save the changes on a regular basis, it was mostly the SLG parts messing around. It also came with the Granada education learning platform for about 25K, which never worked correctly!
Then we upgraded to SLGv2 and lost the learning platform as Granada stonewalled our LEA about releasing it, it simply didn't work on v2.
So one of our deputy heads delivered an ultimatum to the LEA "get it working or get it out!" so they tore it out. We've still got the SLG but it's secondary and with remote access is really being superceded.
At that time I'd been talking about Moodle for 10 years, primarily as a means of delivering homework rather than a classroom thing, the only reason they chose the SLG was for the SIMS integration which Moodle didn't have. So once the Granada platform was removed I "stepped into the breach" with v1.9; we got upwards of 2000 students enrolled though it was awkward to use as a teacher.
I've upgraded to 2.4, cleaning out the userlist in the process, and I've got to say that the whole interface is masses easier (when you add Google chrome you literally have drag and drop functionality for courses) and being php based makes it independent of Microsoft. A teacher wants something particular added I can add it if I can find it. In the month that 2.4 has been active, barring teething problems like the https home access not working, we've gone to 175 users with 5 separate departments wanting training in using the new version.
Overall I'd therefore say though it's horses for courses, sharepoint is OK but it's coming from a business environment not a classroom.