Missed the edit window … disregard the above & read this instead:
My firm does a decent amount of MSCRM consulting, and we use it in-house. We are on the insider beta team for the next version.
The answer to your question depends a bunch on which MSCRM vesion they are using. 1.2 is outdated, 3.0 is now current & 4.0 is the current beta.
MSCRM 3.0 and later can be amazingly customized; at bottom it’s a web-configurable RDBMS with built-in standard UI forms, menus & reporting templates, each of which can also be heavily configured. And a corresponding web service API for inter-system operations.
In 1.2 you had mostly additive customization, where it was very hard to not have it smell like a CRM system with customers, vendors, accounts, & sales efforts as the primary exposed business objects.
In 3.0 (there never was a released 2.0) there is a lot more support for subtractive customization and it starts to really be a generic RDBMS+WebUI.
In 4.0 they finish that job & a skilled dev & analyst config team can rework it to look & feel almost nothing like the OOB CRM system. Damn near any business process that is heavy on user input, multi-player human workflow / action tracking & reporting but fairly light on fully automated bulk operations can be modeled up quickly & easily.
So much for facts, on to opinions:
Typically you don’t see MSCRM used as a public-access product. Each user must have a logon & an expensive license. the hosted version (Dynamics CRM Live) is less costly, but still licensed per user AFAIK.
While it is not a closed system, interfacing things to it, such as typical web-based payment acceptance systems, is not trivial. And can’t be done on CRM Live.
MSCRM has no inherent support for time-slot oriented data such as class schedules. That could certainly be configured into it, but it’d be pretty ugly under the skin.
My bottom line …
I’ve used a lot of different MSFT tools & if my mission was a public-facing portal for convention attendees’ typical uses & also fr the portal operator to maintain attendees’records, MSCRM would be very far from my first choice.
If they already have the problem 95% solved, I’d be cautious about suggesting that you throw out the baby. OTOH If somebody was proposing this from scratch today I’d suggest you tell 'em “Go back; it’s probably a trap.”