How to handle version conflict during Update operation

You can use Microsoft.Office.Server.Utilities.EventReceiverUtility class and IsVersionConflictException method. You can find it useful when you use SPWeb.AllProperties for some application counter for example.

SPWeb web = ...;
bool retry = true;
int count = 0;
while (retry)
{
    try
    {
        int lastId = 0
        if (web.AllProperties.ContainsKey("LastId"))
            lastId = (int)web.GetProperty("LastId");
        else
            web.AddProperty("LastId", lastId);

        lastId++;
        web.SetProperty("LastId", lastId);
        retry = false;
    }
    catch (Exception ex)
    {
        if (!EventReceiverUtility.IsVersionConflictException(ex))
            throw;
        if (count > 2)
            throw;
    }
    count++;
}