Well, as others have said there are a lot of right answers here. But I'll add a couple things:

1. I agree with those above saying that transfers aren't typically much more lucrative than 1.5cpp. But it's important to recognize the variance in miles costs in many programs. Sure, a domestic UA flight in coach is likely a bad buy...but business across an ocean at saver level is likely to be sky-high if you calculate it by the cash price. So, I guess as far as transfers go it's kind of hit or miss.

2. The good news is the portal is an always-available backup, so if you're looking at stuff with low cash prices and high miles prices, you end up coming out pretty well. The flip-side to an airline's awards having low cpp is that cash-equivalents' relative value increases.

3. Also notable is how useful the portal can be for status chasers like me. Tickets bought that way earn me EQM/EQD where a transfer wouldn't; that's a fair bit of extra value in my opinion. Moreover, some tickets in the portal are bulk fares, which earn EQD by distance instead of fare...I've had a few cheap/long bulk fares that earned more than 2.5EQD/$ which helps beef up my competitiveness in the upgrades game.

So, because of these things (and the fact that actually doing the transfers is a bit of a pain, especially if you don't normally work with said airlines and/or have accounts with them) I have spent the vast bulk of my UR through the portal. I've gotten some great deals...DFW-HKG rt for 46k UR, then cleared SWU both ways, bulk fare that earned a ton at AA. Sure, the cash price was cheap, but that doesn't change the actual utility I got from the ticket. If I had bought it with cash I'd have considered it a great deal, so it was a great deal in the portal too.