Magento should probably have APC Cache rather than XCache loaded by Default

[Landis]

Both Magento themselves and Yireo (MageBridge) strongly recomend APC Cache as the default Cache method for Magento. Magento says " Other bytecode cache systems are not supported at this time. "... however Yireo Reports:
Use a PHP accelerator
By opcode caching, PHP-execution could be fastened. There are various PHP accelerators doing this job (APC, ZendOptimizer+, eAccelerator, XCache). Both APC and ZendOptimizer+ are working flawless with Magento.

See two links below:

http://www.magentocommerce.com/wiki/1_-_installation_and_configuration/magento_installation_guide
3 - PHP 5.2.0 or newer, with the following extensions/addons:

    PDO/MySQL
    MySQLi
    mcrypt
    mhash
    simplexml
    DOM

4 - MySQL 4.1.20 or newer

    InnoDB storage engine

5 - Sendmail-compatible Mail Transfer Agent (MTA)

    Magento will connect directly to an SMTP server if you don’t have an MTA

We also recommend the use of APC as a bytecode cache for performance improvements. You can find it in the PECL archives here: http://pecl.php.net/package/APC. Other bytecode cache systems are not supported at this time. TEO DNS resolution (important when installing on localhost)

http://www.yireo.com/tutorials/magebridge/hosting/586-performance-tuning-with-magebridge
and
http://www.yireo.com/tutorials/magento/magento-administration/1056-magento-spo
Use a PHP accelerator
By opcode caching, PHP-execution could be fastened. There are various PHP accelerators doing this job (APC, ZendOptimizer+, eAccelerator, XCache). Both APC and ZendOptimizer+ are working flawless with Magento.

Final Note:
A while ago I was not able to get APC to take the place of XCACHE on 11.1 Magento System. XCache might be fine.. but this seems a subject as our Magento Performance has been extremely SLOW.

something to consider

[Jeremy Davis (jedmeister)]

This probably also applies to the comments that I just made on your other bug report.

I think the difficulty with this sort of thing is that as much as possible, the TKL devs try to make the appliances consistent. Whilst this means that in some cases they may not be ideal, or optimised, maintenance and bug fixes are generally easier (eg all appliances are based on Core, then most of the web app type appliances are based on LAMP). So if there were a good case for using an alternative php caching/optimising app across the board (ie LAMP/LAPP and all derivatives) then perhaps they'll think about it.

[Alon Swartz (alonswartz)]

It is possible to transition to APC, but as Jeremy pointed out, we try to standardize for consistency and simplicity. OTOH, if Xcache does not work, or if APC does in fact improve performance drastically on Magento, then that makes the case to use APC.

Case in point, if we could get benchmarks of Xcache vs. APC on the same installation of Magento (not generic benchmarks), that show a drastic improvement, then I'd be willing to perform the transition.