There have been some flaws with Lion, and I'm not sure how much they've updated since I'm still running Snow Leopard.
BUT, depending on when you decide to buy a new mac, it may have Mountain Lion on it. Although they haven't set a release date yet, but it's a guess that it will be sometime this summer.
I guess it depends on what you're running on your mac. I heard Lion had issues with CS5 and so I hesitated upgrading, but with that being said I haven't checked to see if those issues have been fixed or not.