I don't know who Dell's ODM is, but it is my understanding that the chipset is Marvell and the software is from Radware, who got bought by Marvell. I would be very surprised if the board design differs substantially from Marvell's reference design.
Earlier Dell switches were Broadcom chipset and my experience with those was substantially better than my experience with their current products. I would say the same thing about their current networking products as I would for their other current products - they have their place in the market, and as long as you are getting them for cheap and using the cheap solution is appropriate for the problem, they will meet those expectations.
In my opinion, today, business critical = Cisco or Juniper. Force10 can't quite succeed or fail, and Arista is worth watching, but that's about it. Extreme, Foundry, Riverstone/Enterasys, and 3Com are no longer interesting. HP networking is busy digesting 3Com and their product line is currently a mess that I would avoid until that process sorts itself out.
I haven't really been able to find a current low-end switch I like