First, I'm sorry for the late reply, but I somehow missed this and a few other posts.
For the "standard" BOS configuration - one that uses only the DevForce section config settings or the web.config sample we've provided - we set various quotas to maximum values. Unfortunately, the MaxStringContentLength ReaderQuota is not something we currently set, but I've opened a bug report to address this.
The workaround is to change the reader quotas on the binding via the config file. If you're hosting your BOS in IIS, this is easy to do, since the system.ServiceModel configuration section is defined in the web.config. If you're hosting in either the console or service applications provided with DevForce, this is a little harder since you're probably not using a serviceModel configuration section. I can provide a sample upon request.
Here's the binding change:
<bindings>
<customBinding>
<binding name="compressedBinaryBinding">
<gzipMessageEncoding>
<readerQuotas
maxArrayLength="2147483647" maxDepth="2147483647"
maxStringContentLength="your limit"
/>
</gzipMessageEncoding>
<httpTransport maxReceivedMessageSize="2147483647"/>
</binding>
</customBinding>
</bindings>