Survival represents a character’s ability to track things, to predict and prepare for weather, and to get along in the wild via foraging, and finding food and shelter.
What can you do with this skill?
You can predict the weather, grant some bonuses on saves vs. same, and forage for food and shelter while avoiding getting lost. You can also track creatures.
Everything you can do with Survival besides tracking is pointless. Unless you’re running a very low level campaign where the point is to get the characters lost and starving in the wilds, how often do you think you’ll see this skill used for anything that’s not tracking? Hell, many GMs don’t even track food, so there’s something you’ll never need to worry about. In most cases, if a character says that they have survival skill then that’s good enough – there’s really little point to rolling Survival in any event, since you can (and should) take 10. A 1st level Ranger with 1 rank, and a wisdom of 12 (and it should be at least this, unless you don’t use spells) has a Survival bonus of +5. Taking 10 nets a 15, which passes all non-tracking uses of the skill. So why roll? Just let them be bad-ass survivalists if they want to, and don’t waste time with anything that’s not tracking. Even if you want there to be some chance for the characters to get lost, is it worth wasting time with this?
And then… there’s the weather. Modern weather prediction methods aren’t as accurate or as reliable as the Survival skill. This may be totally irrelevant – how often does the weather matter in your campaigns? But if it does, no more than one days’ prediction should be allowed without magic, and the characters should never be too sure they got it right.
So Survival is basically the tracking skill, right? Well, yes and no. Remember earlier when I said to just let the characters be bad-ass survivalists? So long as they take Survival, that’s fine. We could decouple tracking from Survival, but that seems like too much work. If someone wants to be a great tracker, they’ll need to keep putting point into Survival, and if it ever matters, the character with the higher rank should quite obviously be the badder bad-ass. For the most part, however, 1 rank of Survival is plenty for all non-tracking uses of the skill. If you want to roll, that’s fine, but I’m sure there are better uses of your time.
Final Analysis: If someone has one rank in Survival, they can do all that pointless crap other than tracking. Don’t bother rolling. Tracking is a pretty good use for the skill. So we keep Survival, we just don’t waste time rolling for stuff that should be hand-waved away or negotiated.
Use Magic Device represents a character’s ability to utilize correctly magical items and devices not normally permitted to characters of that class, for whatever reasons (race, lack of training, alignment, etc.)
What can you do with this skill?
You can use magical devices that you’re not supposed to. If you’re a Wizard, that isn’t much; if you’re a Barbarian, that’s a whole bunch of stuff. Scrolls, wands, Holy Avengers; you name it, you can spoof it with this skill.
So who doesn’t like this skill? It has tradition behind it. It’s fun. It appears in literature over and over again. It meets the requirements for when we should pick up the dice.
I confess that even as I like UMD, I’ve always found that this skill suffers from a lack of description. How do you fool the device? What do you say? What do you do? The system abstracts the casting of spells by the professionals, so it’s not like the amateur users of magical devices have any responsibility to ham it up when using the skill. Still, it’s always bugged me a little that a Holy Avenger can know who to smite when it hits an opponent, but can be fooled by the vilest of scum if they have enough Charisma and skill ranks to roll well. And what about intelligent items? Shouldn’t they be harder to fool?
The other issue with UMD is the fact that it’s Charisma based. Sure, that makes sense in many cases, but it also means that dwarven genius wizards will have a harder time figuring out how to use a wand of searing light than a somewhat dim but likeable barbarian. Justifiable? Maybe. It seems to me that this skill could just as justifiably be Intelligence based. Sure, fooling a Talisman of Ultimate Evil requires panache and confidence, but surely being smart would help? For now, I consider Charisma to be the better choice, based on the current mechanics. It also gives Charisma something else to do; it’s still quite the popular dump-stat in many campaigns. Charisma is an awesome stat; it’s the one most useful stat in the “real world”, and I think it gets short shrift in 3e games (it’s totally awesome in OSR, mechanically speaking, and we need more of that awesomeness in Pathfinder).
Final Analysis: Use Magic Device works mostly as is, although I would add 10 to any roll made to influence an intelligent item. It’s a quick fix, but you probably won’t need it all that much, and you can just use the skill as is if you don’t like it. UMD has high enough thresholds that even the fact that they’re static doesn’t unbalance the skill; to use this consistently you really do have to push it up as high as you can, and the penalties can (and should) be gruesome, depending on what you’re trying to do.