actually tends to work very well.
Access fails as a multi user system because it's not client server. IIS (presumably) most definitely is, so access only sees one user and all it's weaknesses in this regard are obviated. It's a very elegant solution until the database slows down due to volume or complexity.
Swapping out access as a backend for SQL Server tends to be trivial, even shifting to MySQL isn't too off putting, should it become desirable.
I've talked to guy one here who does this a lot and he said he got acceptable performance on 50 users and 100s of megabytes of data. No experience of it myself as I tend to do big systems.
As always with client server, the trick is to get in and out quick, minimising the amount of time data is locked.