Speaking from someone who works with health insurance every day: Not much at all.
After June 1, there are certain Medigap plans that won't be offered (I think four of them) and two new ones added. No matter what, if you mother and aunt are happy with their coverage, they just need to continue to pay their premiums and will be fine... whether their particular plans is no longer being offered to new enrollees or not.
Their part D coverage will in all likelihood get better. The coverage gap (or "donut hole") will be eliminated. This is a big big deal if they are on pricey medications. What people are concerned about are those retirees who have their part D plans supplimented by a previous employer (using federal money). Those benefits are now taxed to the employer, starting in 2011. The concern is that the additional tax burden will cause companies to eliminate this benefit to future retirees.
So for you aunt and mom, pretty much business as usual!
I personally don't mind the cap on HSA accounts. $2500 should be more than enough money to be sheltered for medical expenses for most folks who have insurance.