When I attempt to connect to the our server: http://server:3333/SlxMobile/ it failes with an error of 'a problem occurred on the server'.  This descriptive error made troubleshooting easy...  

I have installed SP3 without any errors.  We use SLXClient and SLXCustomerPortal web portals both of which work fine.  I followed the attached PDF's to install all three hotfixes and bundles.  All installed without a hitch.  I removed the Sage.common.syndication.json.dll as noted in hotfix 3 from all the portals.  I then installed Sage SalesLogix Mobile 2011 R1 and bundle this worked as well.  I made the IIS 7.0 changes (through I was unabel to find this setting: enable default content page?)  Anyone know where this is?  Rebuilt web platform.  Redeployed all portals.  Checked Event Viewer and logs were clean.  Other portals installed worked but SLXMobile still does not.

Some of other forums mentioned the default location of SData> C:\Devel\ProdVFS\Model\Portal\sdata.  Is this the default?  I do not recall ever changing this or this being an issue.

http://<servername>/sdata/$system/adapters This returns a <authentication mode="None" />.  I look under IIS authentication and only see 'Anonymous, ASP and Forms'.  Hotfix 3 PDF mentioned more authentication types that do not appear for us.  Is this an issue?

Any one else have any other ideas?  Does the mobile client need addtional hotfixes to be installed?  Anything else I missed?

These two other posts had some other useful informaiton in them:

http://www.slxdeveloper.com/forum.aspx?forumid=4002&postid=28550

http://crm.ittoolbox.com/groups/technical-functional/saleslogix-l/log-on-problem-with-saleslogix-753-and-saleslogix-mobile-new-2011-r1-4141823

This was a tricky one.  I was able to get the above to work after a few months...

The key here was two items ensuring our SData was correct and IIS authentication.  

SData

Assuming you have this setup correctly.  The directions for this are fairly lengthy, if you need these let me know and I can post them.  I will just go into authentication for now since most users probably have their sData correct, I believe we were the exception in this case.  Documentation for setting this correct is in the SLX Guide.  During the initial setup I did not follow this step close enough.   

So once you get your http://<servername>/sdata/$system/adapters displaying data you are only half way there.  At least we were.

IIS authentication is the next important part.  One of these items where after you complete it is easy but trying the different settings was lengthy.  In IIS > Sites> Sales Logix> sData> Authentication> Anonymous Authentication> set this to enabled.  Everything should be set to disabled.  Do the same for SLX Mobile site.  After the change run an IIS reset.  This is the combination that worked for us.  My guess is your authentication settings could be the same or slightly different.  First step get the sData working.  If you are not seeing data on the above link, fix this first, then play around with authentication for the two sites.