First of all, PC and hardware manufacturers can continue to sell the stockpile of Windows XP copies they might have, even after the 30 June cut-off date. The same obviously applies for local retailers; as long as they bought a stock of Windows XP licenses prior to the cut-off dat, they are free to sell them.
The second loophole has to do with something called downgrade rights - we already covered this loophole earlier when it became known. The gist is that within Vista Ultimate and Business licenses, there is a clause that allows you to continue to run an older version of Windows until you are ready to move to Windows Vista.
Ultra-low-cost-PCs or netbooks or whatever they're called today (I lost track) lovers are generally in luck: Microsoft has extended the lifetime of Windows XP for these devices until June 2010, more or less admitting that Windows Vista simply doesn't cut it for these limited devices. In fact, in order to compete with Linux in this niche of the market, Microsoft is offering discounts to OEMs.
A remaining issue is that of support. After the cut-off date, Microsoft will continue to release security fixes and public bug fixes for Windows XP until April 14, 2009. You can have paid support, and warranty claims are still valid. After that, and until April 8th, 2014, the company will only issue security updates, but no more public bug fixes (only companies with a support contract will receive bug fixes). Paid support is available, warranty claims will be void.