By default, if I have a class called "MyClass" it is serialized into a
collection called "myclass"

Is there a way of overriding this in the BsonClassMap?
For example, an attribute on the class, or a Convention?

If not, I'm happy to fork this and try and implement.
Just don't want to double up...

That doesn't currently exist and you must specify this value everytime.
 There is a Jira for this feature:  
https://jira.mongodb.org/browse/CSHARP-126. It is important, vote it up or
leave a comment.

[AttributeUsage(AttributeTargets.Class, Inherited = true)]
    public class CollectionName : Attribute
    {
        /// <summary>
        /// Initializes a new instance of the CollectionName class
attribute with the desired name.
        /// </summary>
        /// <param name="value">Name of the collection.</param>
        public CollectionName(string value)
        {
            if (string.IsNullOrWhiteSpace(value))
            {
                throw new ArgumentException("Empty collectionname not
allowed", "value");
            }

            Name = value;
        }

        /// <summary>
        /// Gets the name of the collection.
        /// </summary>
        /// <value>The name of the collection.</value>
        public string Name { get; private set; }
    }

//use

[CollectionName("myclass")]
public class MyClass
{

 public static string GetCollectionName<T>()
        {
            var _att = Attribute.GetCustomAttribute(typeof(T),
typeof(CollectionName));
            string _collectionName = _att != null ?
((CollectionName)_att).Name : typeof(T).Name;

            if (string.IsNullOrEmpty(_collectionName))
            {
                throw new ArgumentException("Collection name cannot be
empty for this entity");
            }
            return _collectionName;
        }